Brief Summary (tl;dr!)
This guide primarily focuses on K-Drive mode without the use of Loyal Merulina, simply because that's the way I enjoy playing her, but it can easily be slotted in place of Preparation if you so choose.
Simply use Merulina Guardian]'s bonus to both keep Merulina healthy and to provide your secondary weapon of choice with additional bonuses. You will need to use a crit-viable secondary weapon for the most benefits.
Note: The Umbral Forma is not necessary. You can slot it in with a basic Intensify or Archon Intensify and be fine.
Remember to keep moving to take advantage of [Yareli]'s passive, granting her 200% Critical Chance to her secondary, additive to mods. It's a free [Creeping Bullseye] for Pistols with no fire rate penalty, so make use of it!
Understanding Merulina
I'm dedicating an entire section of this build to explaining Merulina's mechanics, as understanding them is key to your survivability as [Yareli], as well as being able to adjust this build to suit the content you like doing the most.
When casting Merulina (if she hasn't been used), Yareli will become invincible for a period of four seconds, including the animation time to mount her companion K-Drive (note that this animation cannot be sped up with Casting Speed). Merulina will be spawned and is considered a separate unit than [Yareli], even if you are not using Loyal Merulina. At max rank with 100% strength, it will have a 7,500HP base health pool, modified by Ability Strength (e.g. having 200% Strength will give it a health pool of 15,000). Any damage taken during the invulnerability time (which is not modified by Ability Duration) will add to the health pool, much like [Rhino]'s Iron Skin.
Once the invulnerability period ends, Merulina will redirect 90% of all damage taken by [Yareli] to itself. Damage [Redirection] works essentially in the same way as Damage Reduction, so it can be treated as such, noting that any damage that this source of damage reduction prevents will be inflicted on Merulina instead.
Merulina itself does not benefit from any buffs that provide Damage Reduction, or even Armor. Merulina itself has 50 Ferrite armor (which is about 14.5% DR), which it will use to reduce any damage that gets redirected to it. There is almost no way of increasing this armor... we'll discuss that a bit later.
Even though Merulina cannot benefit from Damage Reduction, [Yareli] herself still can, which is why we use Adaptation to bolster her survivability, which makes a very obvious difference in higher level missions.
It is also good to know that [Yareli] is completely immune to knockdown effects while riding Merulina. [Primed Sure Footed], for free!
Additionally, sources of sprint speed or parkour velocity have no effect when riding merulina.
When dismounting Merulina, either through taking excess damage, recasting the ability, using your melee button, or using the context button when no other options are available (something that can be rather annoying when trying to interact with something), she will enter a dismount animation, where she becomes invulnerable until it ends. If re-casting Merulina at the appropriate timing when the dismount animation finishes, there will be only a brief window in where [Yareli] is exposed without the damage [Redirection] from Merulina. Note that this does NOT happen when using Loyal Merulina, and so it is especially important to pay attention to the health of your ghost-surfing companion!
[Merulina Guardian]
This mod is core to unlocking the potential to [Yareli], no matter if you are using [Loyal Merulina] or not. It allows you to heal Merulina by using Sea Snares to entrap an enemy having them get killed (it doesn't matter if you get the kill or not). The heal amount is affected by Ability Strength. This healing can also trigger Archon Intensify.
If this results in Merulina recovering health, you will gain a 200% Reload Speed and Fire Rate buff for secondary weapons for 20 seconds, modified by Ability Duration (but not Ability Strength). This means that enemies eliminated while Merulina is at full health will not grant the bonus.
Remember: Reload Speed will impact the time it takes to activate most Incarnon weapons.
The Build (Finally!)
There are a lot of things in this build that can be replaced, so I'll take some extra time to explain what the purpose of each part of this build is, and what they could be replaced with.
Aura Mods
[Yareli] is not dependent on aura mods. Here, I have chosen to use Pistol Amp to squeeze some extra damage out of my secondary weapons, as I exclusively use them (as I'm always riding merulina). However, It can be replaced:
- Combat Discipline will ensure that Merulina Guardian always grants its Attack Speed and Reload Speed benefits, which is useful for lower level missions. However, if you constantly find yourself in the line of fire, this mod won't be very impactful.
- Enemy Radar and Loot Detector are quality of life options.
- Pistol Scavenger is useful if you find yourself running out of pistol ammo frequently. With many secondaries, and all of the fire rate buffs this build can provide, this can be an issue for a lot of secondaries, even if they don't normally have ammo issues.
- Corrosive Projection is certainly one of the auras of all time that isn't ever bad.
Mods
The core mods of the build are as such:
- Blind Rage provides a massive buff to our Ability Strength at the cost of Efficiency. For us, this isn't a problem, as Merulina and Sea Snares are inexpensive. The biggest impact is to Aquablades and Riptide. While Aquablades isn't an important skill, Riptide can be useful for crowd control purposes in certain game modes. Just be cautious on how frequently you cast these abilities.
- Primed Flow (which can be replaced by Archon Flow by downranking Preparation by one level or using an additional forma) will offset the penalty to efficiency. Additionally, the energy maximum is high enough to meet the condition for certain Incarnon evolutions that require 700 Energy, such as the Angstrum's incarnon.
- Transient Fortitude further increases Strength at the cost of Duration, which is offset by Continuity to keep our Duration at about 100%, which is a good sweet spot for Yareli.
- Adaptation will greatly reduce the damage that Yareli takes in general. You still gather stacks when riding Merulina!
The flexible mods are as such:
- Coaction Drift is not strictly speaking necessary. You can skip the exilus adapter completely if you don't care, or forma it to put Preparation there for an additional "real" mod slot. You can get pretty creative here, though. Just remember that movement mods won't have any effect when riding Merulina, and she has no use for Knockdown Resistance or Stagger Recovery. Vigilante Pursuit could be an interesting choice.
- Preparation is the true "flex slot" of this build. Overextended is a very useful tradeoff for your excess Ability Strength for Ability Range, which primarily helps Riptide gather many more enemies for easy pickings. It also improves the seek range of Sea Snares, which is helpful in wide open areas, such as free roam missions or the Undercroft. If you've any other experimental idea, this is certainly the slot to use, which is why it's left unpolarized.
- Umbral Intensify can be replaced with a basic Intensity for low budget builds. It can also be replaced with Archon Intensify - just dismount Merulina once it's been activated with Merulina Guardian and then ride it again, and you'll benefit from an extra (.3*7,500=2,250) health to Merulina!
- Continuity can be replaced with Primed Continuity or Archon Continuity (note that you won't be able to proc the additional benefit the Archon variant provides) by spending an extra forma to [Extend] the buff duration of Merulina Guardian and the duration of Sea Snares and Riptide.
Arcanes
These are also completely Flexible. Replace either of them however you please.
- Arcane Pistoleer is a cheap way to [Extend] how long you can shoot for before reloading or, even worse, running out of ammo entirely. I don't even have this maxed and it's still useful.
- Molt Augmented is good for longer missions to have some extra strength.
- Arcane Velocity is extremely easy to proc given Yareli's passive, and is even more fire rate... don't you think you have enough? Or are you never satisfied? ;)
- Arcane Awakening is good for the same reason as above. More pistol more betterer!
- Arcane Nullifier is good for resisting Magnetic procs, which can mess with Yarelii's survivability.
Archon Shards
Archon Shards are fairly optional on [Yareli]... and yet, they benefit her very strongly. Before I get into the recommendation list, I need to explain something.
Remember how I said there was "almost" no way of increasing the armor of Merulina? Well, there is one, and only one, way of doing so, and that's through the Azure Archon Shard. For WHATEVER reason, this applies to Merulina, too. A single standard shard can take her 50 Armor/14% DR all the way up to 200 Armor/40% DR! Keeping armor scaling in mind, the benefits of doing so will slowly diminish the more of these shards you will use (the absolute maximum you should consider is using four Tauforged shards for 950 armor; anything past that is excessive). That being said, just using one of these will significantly increase the durability of Merulina much more than a Crimson shard set to give Ability Strength will, and that will become more and more true the more Ability Strength you have, unless you already have a significant number of Azure shards installed.
With that out of the way, let's talk shards:
- Crimson shards set to Secondary Critical Chance will stack additively to mods alongside [Yareli]'s passive. Still, for crit weapons, more is better, and using enough of them could even be enough to suppliment a crit chance mod entirely, freeing up a mod slot on your secondary! Or, you could push for those juicy red crits. I won't blame you.
- Amber Shards set to Energy Orb Effectiveness or Energy on Spawn (if you aren't already using Preparation) could very easily solve any energy problems you might have, if you even have any to begin with. Still, this is very optional, and I personally don't run them.
- Azure Archon Shards set to Armor is what I explained up earlier.
- Topaz Shards set to Secondary Crit Chance on Kills Against Enemies Affected by Heat is a good scaling alternative to normal Crimson Archon Shards, but locks you in to using secondaries with Heat damage.
- Emerald Shards set to +2 Max Corrosion Stacks is an obligatory "hehe armor strip" option for those Corrosive weapon lovers out there.
Secondary Weapons
Yareli loves weapons that don't require a huge amount of precision, and have a high base crit chance/damage, and benefit from her fire rate buffs. Incarnon weapons tend to be good candidates, as Sea Snares is very helpful in lining up enemies to easily be shot to charge them. I personally use the Prisma Angstrum incarnon, as it builds up extremely quickly and benefits from the fire rate buffs and has a good crit to boot. However, I encourage you to experiment! There's actually quite a few weapons out there with decent crit, so just try stuff!
Companions
I recommend building a MOA with high shields for Reinforced Bond with a [Vulcax] or [Vulklok] for Tenacious Bond for the additional bonuses to Fire Rate and Critical Damage, just to really crank things up to 11. You could totally experiment with this too, though.
Conclusion
[Yareli] is perfectly survivable overall, but her damage output depends heavily upon having a good secondary that is built for dealing damage rather than acting as a primer. This, on top of the K-Drive gameplay and the bugs that come associated with it, can turn people off from her, or relegating her as a warframe that relies on an augment that turns off her main gimmick. And so, I leave you with some miscellaneous tips that might change your mind!
- [Yareli] is excellent for soloing a Netracell mission. While riding Merulina, none of the keyglyphs will have any effect on her (but will still affect your Operator) with the exception of the storm keyglyph that shocks her (while shocked, she will be unable to fire her weapon). So long as you dodge those, you'll be able to sub-10 these missions fairly comfortably once you get used to the K-Drive controls.
- She can also comfortably do Conjunction Survival, as Occulysts cannot scan her while riding Merulina. If you'd still like for the sentients to spawn, let them scan your operator instead.
- As of a recent patch, she can't die while your operator is out doing things, but Merulina can still break. Use Vazarin's Protective Sling if you're concerned about transferrencing back in and dying, or just go somewhere else.
- Tapping sprint will let her roll while riding Merulina. This can be done in the air or on the ground, and is useful for interrupting falls, gaining speed from neutral, or barreling through a group of enemies you'd normally collide with.
- Refrain from shooting for a little bit if you'd like to unlock the full speed of your k-drive's sprint. You can even tap your use key to put your gun away and perform normal K-Drive tricks and earn Ventkids standing while in missions, if you'd like.
- Yareli cannot get knocked off her k-drive unless and until you either run out of health with it, or dismount her yourself. This means you won't "wipe out" if you fail a trick, you won't get knocked down or back by any means, and you don't even need to worry about stagger.
- Yareli can do many things that can't normally be done on a K-Drive, such as hacking terminals. The main thing she can't do is revive someone, so enter your operator form to do this.
