Probably the most solid build I've tried on [Yareli].
Don't want to die? Just say no. Aqua Blades are a guaranteed stagger, while Merulina provides 75% damage reduction. You are invulnerable while mounting or dismounting Merulina, so you can keep that reduction up permanently.
Use Viral from your secondary weapon as a primer, and let Aqua Blades do the rest. Works in steel path (Especially in steel path) with no issues provided you group all enemies. Luckily, [Yareli] has that covered too with her Riptide.
Exilus Slot has only 1 option unless you want to use an umbral forma here, and that's [Power Drift]. The extra Ability Strength is nice, and outperforms almost any other option.
Aura is [Pistol Amp], since [Yareli] is a frame that is restricted to her secondary most of the time. It is important to note that beam weapons may not work properly on Merulina, so weapons like the [Atomos] should be avoided. This was an issue on her release, and hasn't been addressed in any patch notes, but may have been fixed. Testing is required.
For mods, we have [Augur Secrets] and [Umbral Intensify] for Ability Strength. This allows us a lot of damage on all of our abilities, but more importantly, about 14,000 health on Merulina.
For tankiness, we have [Umbral Vitality] and [Adaptation]. [Augur Secrets] also helps here a bit due to the set passive. Merulina tanks 90% of damage we take, and on top of that, [Adaptation] still stacks on top of that, meaning as long as we are on Merulina we take little to no damage.
Finally, for duration to help our Aqua Blades, we have [Primed Continuity]. If you want more, you can replace [Augur Secrets] with [Augur Message], which adds about 10 seconds to the duration. [Surging Blades] is an insane augment that buffs our damage to a massive degree. Note that it only buffs blades you throw with it's active, not your passive blades.
And to ensure that our abilities are always castable, [Primed Flow] and [Streamline]. Not much to say here.
Archon Shards: With this build, I highly recommend Archon Shards go to either Armor if using Azures, or Duration, if using Crimson.
HUGE buff to [Yareli] as of today's Update: Merulina now soaks 90% of damage rather than 75%. This is a massive change that ups [Yareli]'s Survivability!
ANOTHER big buff to [Yareli], as Shields and Shield Gating have been buffed! It now takes even longer to smash through her defenses!