Arknights Mostima Guide

by Zemanius

Recently, Mostima was labeled as the weakest 6 star by the NGA forums on EN. As a avid Mostima user and someone who currently has way too much time on his hands, I’ve figured that this would be a good time to write an extensive guide on Mostima after much research and experimentation to hopefully let people know that Mostima can be a really good unit as long as you know how to properly utilize her kit in the correct situation.


First of all, I need to set the facts straight: Mostima is not easy (and can be sometimes awkward) to use. In fact, if you’re deciding whether or not to roll for her when her next standard banner comes for gameplay purposes (which I believe is soon as Mostima is released after Schwarz), I would suggest you borrow someone else’s Mostima first and try her out before committing to it. Her average dps is so low that it massively guts her from being used as a generalist. Stages where she can fully display her strengths are also not very common. In fact, the way she is used seems to be more reminiscent of a specialist than a caster, but I digress. This guide isn’t discussing about how good Mostima is for general use. This guide is simply here to help you to get the most out of her by making full use of her unique kit, while also giving a balanced view about her strengths and weaknesses. With that out of the way, let’s get started.

In short, Mostima is an arts AOE specialist caster with characteristics that are in line with that class archetype. As such, she is cursed with a small 3×3 attack range with an extremely high dp cost of 34 and low dps. This is due to her high damage per hit alongside a massive attack interval of 2.9s. In fact, at e2 40 with 100% trust she has 788 attack but only 292 dps. She just isn’t fit for doing damage. Thankfully, just as the tags for her suggest (AOE/Support/Crowd Control), she makes up for it due to her talents and skills which provides a huge amount of utility especially when the situation calls for it. In fact, the things she can potentially do are so one of a kind that she opens up many strategies that other operators can’t possibly replicate.


Talent 1: Skill Aura-Caster

+Increase sp regen rate for all casters by 0.4sp/sec as long as she is deployed in the map, including herself.

-Will not stack with similar effects such as Ptilopsis’ talent (but it will stack with different ones such as Ifrit’s).

This is a very strong talent for casters, allowing them to spam their skills more often and is more important than it sounds as most casters have bonus effects tied to their skill usage (such as resist reduction for Eyja’s s2 and Ifrit’s s3). This can indirectly boost the damage output of your team much more than what you would expect, especially if you are using the aforementioned units.

Additionally, this passive is really important on Mostima herself, as her skill cooldowns are intentionally balanced around this increased sp regen, having unusually higher sp costs. However, this form of balancing can be a double edged sword, depending on how you view it. On one hand, this passive reduces her cool down duration to be a lot more manageable and normal. On the other hand, unlike other units whose skills are balanced around the default sp regen rate, it can sometimes feel as if her skills don’t charge up fast enough given the strength of this passive. To put it simply, your other casters will have their skills ready faster than normal, while Mostima will take a “normal” duration to do so. This might mess up with timing and skill rotations in tight situations, where your other units will have their skills ready but Mostima will not.

Talent 2: Subjective Time Dilation

+Slows all targets that enters her attack range by 15% (18% at pot 5).

With this talent, enemies will basically take 1.18x (1.22x at pot 5) as much time to walk past her compared to normal. In other words, an enemy that normally travels 7 tiles will basically only travel about 6 in the same duration while under Mostima’s slow. In theory, this slow seems pretty strong. A normal slow supporter without any skills slows an enemy for 0.8s by 80% every 1.9s, which means an enemy slowed by your average supporter will move at an average of 66.3% normal movement speed. A slow supporter’s slows becomes a lot less potent as the number of enemy it targets increases (since it has to alternate its attacks between all enemies present), with the average movement speed of enemies increasing to 83.2% for 2 and 88.8% for 3. Mostima does not suffer from this problem, since her slow is aura based. All enemies in her attack range will be slowed by the same amount, regardless of the number of enemies present. In other words, her slow is better than a slow supporter slowing 3 units at once but very slightly worse (actually better at pot5) than one slowing 2.

While this passive slow seems useful in theory, in practice the 15% slow (or 18% extra time taken) is so minuscule that you might not even notice the enemy slow down unless you observe carefully. This combined with mostima’s poor attack range means that she will usually only delay the enemy by a second or two at most before the enemy reaches your frontline, making its usefulness fairly limited. Nevertheless, there will be times where this spilt second is life saving, especially when slow moving but heavy hitting enemies are concerned. After all, as minuscule as it is, that’s still 18% extra time (or 22% for p5) that enemies will spend walking within the attack ranges of your operators where all the damage you deal come from, assuming you position Mostima accordingly.

Furthermore, there’s a hidden aspect to this slow that’s not being mentioned enough: It’s ability to basically counter Defense Crushers! Apparently, the slow, while seeming minor at first glance, is just enough for units stunned by a Crusher to recover before it moves past them. It other words, with Mostima, Defense Crushers will need to get in 2 stuns (3 for Blaze and other units with “resist” trait) to bypass your units, and that is more than enough time for your units to take it down before that happens. This aspect makes Mostima’s second talent a lot more useful than it meets the eye. When it comes to Defense Crushers that is.


In this section I will give a detailed analysis on her skills, alongside various techniques and opportunities that you can use each skill on. Note that some of these techniques may be quite situational and thus not see much use. This is what happens when you sacrifice damage for utility, unfortunately. You don’t need a support most of the time when you can just instead field in another dps. Nevertheless, using Mostima’s skills properly when the situation calls for it can still aid your team immensely.

Skill 1: Attack Up

+For 30 seconds, increases her attack damage by up to 100%

+Low sp cost of 30 at max mastery combined with her sp regen passive gives her a high skill uptime

-Only increases damage

Additional Information

Generally, this skill isn’t worth taking, since her base dps is already quite low to start with. Additionally, it provides no additional utilities whatsoever, which is what you mainly use Mostima for. Skill 2 and 3 are better skills for her to use and brings more to the table. For the sake for not making this guide any more longer, let’s just move on.

Skill 2: Lock of Desolate Time

+Stuns enemies for up to 7 seconds at M3

+Does high burst damage, doing up to 140% dmg per second

•Moderate sp cost of 50 at max mastery.

-Hard countered by enemies that are stun immune

Additional information

If you are aiming for masteries, I highly recommend you at least M2 this skill, as it extends the stun by 1 additional second, making 7 seconds her maximum limit.

Having has a sp cost of 50 and a moderate cooldown time of 35.7s, you should be able to have it up for every tough enemy wave most of the time. This is why s2 is the skill that people most commonly use. Do note that timings may still get quite tight at times, but it can be managed.

This skill also packs a large amount of damage, dealing a total of 980% arts damage at M3. This extremely high damage multiplier coupled with Mostima’s high attack stat might as well make her an honorary nuker. A 100 trust e2 40 mostima would basically do 7722 damage. For comparison, Chen at the same level and trust at M3 would do 6100 damage. The only things preventing Mostima from becoming a full on nuker is her skill cooldown time which is slightly too long for a 7.7k damage nuke and inability for her to be deployed flexibly and instant casted. Also, did I mention that this damage is fully multiplicative, which means it synergies really well with buffers like Warfarin? Despite all this, her damage isn’t the main highlight of the skill. The stun is.

Having a 7 second stun is huge. It is the longest form of hard crowd control in the whole game , and by a long shot (Edit: 2nd Longest in CN, because Eunectes). This stun can do a lot of things. Mainly, it buys time for you to kill hard hitting enemies before they have a chance to wreck havoc on your units. To make things even better, this skill is “retroactive”, and any enemies that enter her attack range while the skill is up will also take damage and get stunned for the remainder of her skill. This has the added bonus of causing enemies to clump up together especially at the edge of her attack range, increasing the effectiveness of your AOE units. Therefore, this skill should be used as an supportive ability and not a standalone one, providing you an opportunity for your other units to do work on the enemies without any danger. That being said, these are some ways to use s2 that you can employ to be make better use of the stun.

Techniques/Situations to use this skill

  1. Stalling dangerous enemies that you don’t want touching your frontline. This is obvious. When you can’t tank, just stall, and Mostima’s s2 is really good at that.
  2. Creating temporary chokepoints at kill zones. This is an application of stalling, but for this one you aim to stall an enemy in your kill zone without the use of a blocker. This is useful in situations where enemy elites comes in intervals allowing you to cycle your s2 in time and you can’t really place your blockers and dps units close to each other. Example
  3. Just before an enemy hits your units/before your units die. This interrupts and resets the enemy’s attack animation, which buys a small amount of time which may be useful in edge cases. Useful when you encounter hard hitting elites with long attack animations. You can take it one step further by delaying your activation until your units are almost going to die, which involves your healers. The 7 second stun is more than enough for your medics to heal up everyone fully by the time the stun ends.
  4. When you’re using melee units that can self stun (E.g Specter, Liskarm etc). Using s2 right as soon as their self stuns kick in allows you to stall the approaching enemies until your units recover. With this added safety, you can afford to spam their skills more aggressively. This works especially well with Specter, as Mostima’s stun can basically prevent those annoying situations where Specter dies immediately after her immortality ends. Despite her self stun being 3 seconds longer than the duration of Mostima’s s2 at M2+, this is not really an issue as most mobs save for the faster ones are unable to pass through her within the 3 second downtime (Also remember Mostima’s passive slow?). Ultimately, this combo can stall enemies for up to a staggering 22 seconds!
  5. Spiltboxing enemies. Have Schwarz and Ifrit on adjacent lanes due to tile constraints? No problem! Just place Mostima in such a way that the edge of her attack range is between the tiles you want the enemy to be spiltboxed at, and cast s2 just before the enemy enters Mostima’s attack range. You might miss a tick of damage or two, but it doesn’t matter because the enemy will most likely be dead before the stun even ends. As a bonus, it spiltboxes all other enemies that enters it as well. This method has a few flaws though. The awkward placement of Mostima means that you might not be able to take full advantage of her normal attacks and passive slow. Additionally, faster moving enemies like Breakers have a chance to not be spiltboxed correctly, if Mostima’s periodic stun procs fail to catch them in time. However, most bosses and threatening enemies tend to be slower moving so the spiltbox failing shouldn’t be too much of a problem. Example
  6. Spiltboxing inside Mostima’s attack range. You can spiltbox the enemy too if it is timed well enough while the enemy is inside Mostima’s attack range and just about to walk between 2 tiles. It can be quite difficult to get the timing right, but I find that looking at the enemies’ shadow helps. It is also harder to do it while the enemy is moving vertically due to perspective. An easier way to do it would be to just use a unit (preferably a fast redeploy one) to spiltbox the enemy between the 2 tiles before using her s2. Ensure that you do this before the enemy makes contact with your frontline operators though, as the enemy cannot be spiltboxed once that happens. Note that when using this method, any other enemies that are going to enter the edge of Mostima’s attack range while the skill is active would just get spiltboxed there which might not be the area you want them to be spiltboxed in, though that can be seen as a strength if you want your units to focus fire only on those enemies spiltboxed inside.

At this point, it is totally okay for one to cast s2 earlier than intended to get s2 ready for subsequent waves. It is also good to note that this skill has one fatal weakness: Stun resist. Some enemies and bosses cannot be stunned and will be able to invade Mostima’s world of stopped time, negating the main highlight of her s2. That basically hard counters this skill. Hypergryph pls let Mostima at least bind stun immune enemies

Edit: To clarify, this skill actually consists of “x” number of 1s stuns, where x refers to the total skill duration. Damage and stun is applied per “beat”. This is why if you remove Mostima while her s2 is active , the stun will almost immediately end.

Edit 2: After much experimentation, I have found out that s2 can very rarely fail to spiltbox slower moving enemies as well. In fact, I had one instance where it failed with a Heavy Defender moving at 0.75 tiles/sec. Regardless, spiltboxing for most enemies should be more or less still consistent. The case with the Heavy Defender (and other slow moving enemies in general) is a pretty extreme example that I tried very hard to make happen and thus shouldn’t occur in normal circumstances unless you’re really unlucky. Nevertheless, if you want to play safe you can always place your stronger dps or AOE unit targeting the spiltbox tile in Mostima’s range (since stunned enemies will always be in that tile) and your weaker or ST unit targeting the one outside (ST units can only hit 1 enemy at a time, so it will still do full dps as long as there is at least 1 spiltboxed enemy).

Skill 3: Key of Chronology

+For up to 27 seconds, increases her damage by up to 170%

+Expands attack range by 1 tile on all sides except the back

+Triples the strength of her second talent, slowing all enemies in range by 45% (54% at pot 5)

+Pushes enemies away from Mostima’s current position with “small” force.

-High sp cost of 110.

Additional Information

Firstly, despite the increase in damage (Up to 2128 per hit at e2 40 M3), her dps is still quite low at 734dps per enemy. This is why her skill 3 cannot be compared to that of Silverash and Eyja for the most part (There is a rare exception where I will explain later). She is hampered by her slow attack speed. She is after all a crowd control unit, not a delete all button.

Secondly, this skill has a really high cooldown time. This is in my opinion the greatest weakness to this skill. This would not be an issue if enemies come in one giant wave. However stages in the game tend to have multiple tough waves instead of one extra tough one. At 110 cost, it takes 78.6 seconds to recharge, which meant that this skill should be reserved only for big waves and is not suitable to deal with constant enemy pressure. You’ll basically only get to use it 1-2 times in a stage most of the time. This is the reason why s3 isn’t used that much compared to s2. Its simply unable to recharge fast enough to deal with multiple waves that are spaced moderately apart that the game is full of. Moreover, unlike Silverash, it is often not worth to use it as a helidrop skill. Even with 80 initial sp at M3, it still takes 91.4 seconds (84.4s with Silverash’s passive) for her M3 to be ready again starting from the moment you retreat her. Therefore, unless you want to retreat her after less than 4 swings (which you shouldn’t), it is better to simply leave her be. Besides, she’ll be able to help other casters with their sp regen while she’s on the field.

Thirdly, enemies in her attack range are now reduced to 55% of their normal speed (46% with pot5). Her passive slow is now better than a normal slow supporter’s targeting a single enemy (66.3%) and it affects everyone in range.

Lastly, it pushes the target away from Mostima with ”small” force. This knockback when combined with her passive slow does amazing things: As along as they aren’t fast enough, it can tilelock enemies with a weight level of 0 on the outer 1-2 tiles of her now expanded attack range (1.6 tiles knockback). This includes enemies such as slugs and wolves. Enemies with a weight level of 1 like soldiers and most casters will be tilelocked on the spot instead (0.4 tile knockback). (Bonus fact: Do you know that the casters in chapter 6 actually have a weight level of 2?) However, do take note that since the knockback is directed away from Mostima’s current position, the angle of the enemy from Mostima will greatly affect how effective the tilelocking actually is (Enemy speed is also another factor, obviously). For best results, try to have Mostima directly face the direction you want the enemy to be knockbacked towards.

Moving on, enemies with weight level of 2 such as Junkmen or the Sarkaz enemies in chapter 4 will take extrememly minor knockback (0.1 tile knockback), while any enemy heavier will be completely immune to it. Regardless, all enemies will still be heavily affected by her passive slow. On the bright side, there is a way we can use this to our advantage, and I will explain it later further down.

Additionally, as long as the enemy can be displaced even just by a little, Mostima’s hits will interrupt their attack animations, fully resetting their current attack and forcing them to wait for their next attack cycle in order to be able to attack again. This property allows Mostima to negate some damage, but her slow attack time causes this to be quite inconsistent and shouldn’t be relied on. This applies to all enemies with weight level 2 or below. Anyone heavier than that will be unaffected by the knockback and thus the attack cancel.

Since this skill’s pushing effects are heavily tied to the enemies’ weight levels, there definitely some level of synergy with Angelina’s s3. Her s3 when active decreases the weight levels of the enemies by 1, allowing Mostima to now attack cancel weight 3 enemies and tile lock weight 2 ones. However, do take note of the potential anti synergy that might occur between the 2 units. Under the influence of Angelina’s s3, it is now entirely possible for Mostima to knockback very light enemies so far back they might not return back into Mostima’s range in time to get hit again, wasting precious dps. Even if that does not happen, Mostima might also knockback light but high priority targets out of range of your other dps units which will definitely not aid in defeating them any faster.

Alright, so that was quite a bit of information, so here’s a simple table summarizing everything.

Weight LevelKnockback ForceCan it Interrupt Attacks?Can it tilelock?
01.6 TilesYesYes, at edge of attack range.
10.4 TilesYesYes
20.1 TilesYesNo

It is also worth mentioning that while skill 3 can be very useful in delaying and crowd controlling mobs, you should be careful when using this skill against ranged ones, for it has its own share of pros and cons. In some cases, the slow and knockback combined may push ranged enemies so far back that they might never get a chance to hit your units at all. On the other hand, it might also cause them to clump up and aggro against your more fragile units if your defenders are out of their attack range which can backfire massively.

So, with skill 2 being more useful overall and skill 3 having its own share of equally potent upsides and downsides, how can we make the latter skill work? Well, there are some situations where you might want to use skill 3 over skill 2.

Techniques/Situations to use this skill

  1. Keeping dangerous enemies like exploding slugs away from your frontline. This is perhaps the most practical and useful application that I have found for her s3. Her extended range combined with her slow and knockback ensures that the slugs for the most part do not get more than 1 tile into Mostima’s range; Do note that due to her slow attack speed, slugs might sometimes get 2 tiles in. However, as long as it survives a hit from Mostima this can be avoided, as it will sync the slug’s movement to her attack timing (Enemies don’t get knockbacked if the attack kills it. ) This comes in really handy in stages like 4-7 where slugs come in large numbers. Slugs are not only the enemies she can cc too. She can buy a huge amount of time for lighter enemies such as the annoying Wraiths. Also, do you know that she can interrupt the binds of Sarkaz Casters too? However, due to their 3 tile bind range, Mostima can only target them if they are in the top part of Mostima attack range where her reach is longest. And also if the chains don’t get Mostima first. Example
  2. Funneling. Dangerous and high priority enemies tend to have higher weight levels compared to weaker ones. Mostima’s s3 allows us to abuse this by allowing only the stronger mobs to get deeper into her attack range while keeping the weaker enemies further away. This allows your dps units especially single target ones to focus only on the enemies that truly count, instead of wasting damage on trash mobs that would have been easily taken care of by aoe attacks, and in this case, Mostima’s. Example
  3. Swarms of enemies. While it may be rather unrealistic, I believe it’s still worth mentioning that there is a specific situation where this skill will have more overall dps than Silverash or Eyja’s s3: When there are many mobs present in her attack range, and by ‘many’ I mean at least more than 10. Unlike those 2, Mostima’s s3 does not have a cap on the number of enemies it can hit at once. Stages with such dense enemy counts are extremely rare though, so this use is extremely niche.
  4. Against enemies with stun resist. No enemy is immune to slows, so Mostima’s s3 might come in useful here. However do note that there are better units that you can use instead (like Angelina) if you only want the slow and not the other additional effects that Mostima brings to the table.

Should you be aiming for masteries, I would recommend you to at least M1 this skill even if you don’t use it that much as it enables her to get 1 more attack during her s3, up to a total of 9 times. If you find yourself using her with Angelina a lot and are willing to invest a little bit more though, getting her to M2 is pretty nice too as Angelina’s passive attack speed buff will just allow Mostima to get 1 additional swing in, giving her a total of 10 attacks instead. Unfortunately M3 does not increase the number of attacks she does, regardless if Angelina is present or not.


We’re finally at the end of the guide! If you‘re still here, congratulations for making it through this wall of text. In conclusion, Mostima is a AOE crowd control caster that has a high skill ceiling on how you utilize her kit, but she opens up a large amount of unique strategies for your team if you use her right. However, she is at the end of the day still an enabler that cannot really stand well on her own. Her effectiveness greatly depends on what the rest of your team can do while you can do while her skills are active, and for most stages you don’t really meet enemies threatening enough to need some form of crowd control when you can just field in another dps to take them down quicker. The stages in the game are not really made for Mostima to fully display all her strengths. That is not to say that she is useless though. All in all, with enough time and commitment, you can definitely make Mostima work wonders.

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