Was originally going to post this feedback for Yareli as a response to someone but it's more fitting here.
I've been playing with her in Steel Path and Sister hunting, and can confidently say she's all flavor and no substance despite 3 forma and more playtime than Hildryn. I don't know how anyone can consider her even close to okay in her current state. She's fun to play when the enemies can barely penetrate your shield but there's no way I'd feel comfortable bringing her into an Arbitration.
Sea Snares is okay for stalling super bulky units but the damage (which doesn't even apply a status to help with CO or GA) is so insignificant, even with a long duration, that with so much effective HP it may as well be a pure-CC ability. I'd much rather the ramping damage mechanic be replaced with a progressive armor strip or massive vulnerability to Electric procs, just something to keep it relevant in higher levels.
Merulina is a significantly worse version of Warding Halo numbers-wise, with the added downside of being harder to control than old 8DOF archwings in Corpus ships, and it can instantly vanish with any enemy knockdown even when using maxed Prime Sure-Footed. The complete lack of scaling means that my 15k HP Merulina dies almost immediately after spawning if I'm getting hammered by gunfire. Halo can easily scale into the 200k range on longer runs, it gives 95% DR instead of 75%, and Nezha has free access to all the available methods to heal when his meager health pool takes a big hit. Since Merulina restricts you to your secondary when mounted, you're incredibly limited with your healing options. You can't:
take advantage of Life Strike/Healing Return (no melee)
use Protective Dash (no operator)
cast an augmented Molt (no Helminth abilities)
...and none of her abilities offer any form of health regeneration, leaving you with the Rejuvination aura, health pizza, Arcane Grace, and Arcane Victory as your only methods of post-mounted healing. It's impractical to say "weave Merulina in with regular gameplay" because she has almost no survivability on her own two feet. I tried using Gloom in place of Riptide but it's bugged while riding and only her 1 and 3 can heal at the moment. I'm not even going to touch on the fact that it's an unmoddable K-drive because the base ability needs be worth using before talking about its possible bonuses.
Aquablades is bad functionality-wise, and no amount of number inflating will save it from that. It reads and plays like an early Warframe ability, just a flat damage cast-and-forget ability with zero secondary function or synergy, useful only in early star chart missions to give new players the illusion that they're powerful as they run through level 10 lancers. It doesn't provide additional damage resistance, doesn't scatter Sea Snares when hitting an affected target, doesn't deflect incoming projectiles, isn't affected by her equipped melee in any way, it's a source of miniscule melee range slash damage and nothing else. It has the perfect aesthetic to be the conjunctive mitigation ability to Merulina for when we're made vulnerable in its absence.
Riptide has potential to be good outside of early missions, but the disruptive projectile ragdolling needs to go before anything else changes. I feel like it would fit better with Yareli's kit if it had a duration instead of pulling then dissipating at the end of the cast. Even the preview video in the abilities screen makes it look like it draws things in and keeps them there for a time before exploding. By making it duration-based instead, it opens up the possibility of creating some synergy with the kit, such as:
Riding Merulina into a vortex's radius heals it and Yareli by X%/s
Staying within the vortex's radius with Aquablades active keeps the vortex invigorated, freezing its timer
If an enemy affected by Sea Snares is pulled in, all enemies within get affected for the remaining duration ||OR|| Enemies affected by Sea Snares increase the vortex's damage by X%
Enemies within are X% more vulnerable to secondary weapon fire
It really is disappointing seeing how underwhelming she is when her direct predecessor Sevagoth had such an outstanding launch that I felt no regrets plugging 2 Umbra Forma into him in the first day. Yareli by comparison is the equivalent of a disjointed group of kids where one is reading, one is watching TV, one is playing in the pool, and the last is pulling the legs off spiders.