In my [Loyal Merulina] [Yareli] build you'll be sacrificing duration for efficiency to increase the frequency with witch Merulina can cast her Sea Snares, with the goal of stacking Merulina's Sea Snares with our own for insane multiplicative damage vulnerability on as many targets as possible, as often as possible.

Realistically nothing in this build requires a lot of duration to be effective (other than maybe how often you have to press your subsume), so having Merulina spit out bubbles every 0.5 seconds means more chances for us to multiply our damage against enemies considerably. Yay!

Exilus

I went with [Power Drift] here for a little extra Ability Strength and 30% chance to resist knockdown. (You may prefer PSF, but I'm not veteran enough for PSF.)

Mods

• [Transient Fortitude] and Fleeting Expertise help increase my strength and efficiency while sacrificing duration, which is what we're going for
• Primed Continuity makes sure we have decent enough duration
• [Boreal's Hatred] was chosen for increased shield support AND even more Ability Efficiency, lowering Merulina's Sea Snares to her lowest possible cast time of just 0.5 seconds. She's casting Sea Snares with me like crazy, it's :chef's kiss:
• [Energy Nexus] is a nice way to make sure you always have enough energy coming in. With no [Equilibrium] or Arcane Energize on this build, it keeps your energy levels healthy, even when you're spamming bubbles constantly

Arcanes

• Molt Augmented: MOAR STRENGTH RAWR
• Arcane Avenger: More crit chance? Say less

Honestly, Arcane Camisado could be a fun one in place of Arcane Avenger here, too. With Merulina casting every 0.5 seconds, those Ability Strength stacks can get to 60% quickly and consistently. Give it a try!

Subsume: Eclipse over Aquablades (3)

I like the versatility of increasing my weapon damage for most content, but also having the option to boost my damage reduction further if needed in a sticky situation instead of using up a mod slot with something like [Adaptation], so that's why I took Eclipse. You may prefer something else, and that's totally okay. Go with your preferred subsume here, there are so many viable options!

Archon Shards

I use one tauforged amber for +37.5% casting speed, and the rest are tauforged crimson for an additional +60% Ability Strength. Yum!

Focus School

I use Madurai so that one day when I'm good enough to remember to switch to Operator and chain sling a few times and back for a 40% Ability Strength buff or 50% Casting Speed buff I'll have those, but if you're worried about energy and not coordinated enough to make effective use of switching between Operator and Warframe regularly, you may like Zenurik for a little boost to your energy pickups without having to think about it. Whatever you prefer!

Companion

• My Panzer Vulphaphyla build provides viral priming, 60% more fire rate for you, and an additional +1.2x final critical damage multiplier for you, too! Its [Panzer Claws] tear through overguard targets and their shields as if they didn't exist. (The build for Claws is listed on my Panzer build, too) Sweet!

Weapons

• Primary: I like the Cedo Prime for its bouncing glaive alt-fire priming capabilities, but since we focus Secondary weapons due to Yareli's passive, just pick a Primary whose flavor you like
• Secondary: [Kompressa Prime] with the Secondary Enervate arcane, whose critical chance bonus can continue to build up well past 200% because of the bubble explosion delay, so enjoy those silly red numbers. I like Viral, Magnetic, & Blast for the lols
• Melee: Any flavor of the [Furax], as long as you have the [Amalgam Furax Body Count] mod on it to give you an additional 45% fire rate on your Secondary. The rest of its build doesn't matter all that much since you'll be too busy blowing bubbles

Versatility
In my first iteration of this build I had [Archon Flow] in place of [Boreal's Hatred] for a bigger energy pool and a chance to drop more energy orbs, since [Yareli]'s 1 and 4 both do cold damage. However, I've found I really don't need nearly 800 energy, even with casting a lot, so [Archon Flow] felt a bit overkill and [Energy Nexus] was sustaining me fine in Steel Path, which is why I went with [Boreal's Hatred]. So if you find yourself out of energy, you may want to swap [Archon Flow] back in. Just know that Merulina's cast time for Sea Snares will go up to 0.8 seconds with this change, and you'll lose a little bit of shieldgating support and Ability Efficiency. Totally fine in most content if that's more comfy for you!

Thoughts? Something missing? Something that could be better? I'd love your (constructive) feedback. :)