This Guide will include;

• Links to other builds -without guides (a bit about riding Merulina is in about Yareli)
• Build
• Arcanes
• Archon shards
• My secondary choice + link to build + arcane
• Subsume
• About Yareli
• Hints

I have various builds for Yareli for different things. This is the only one I'll do with guide.

Merulina Guardian :
https://overframe.gg/build/856408/yareli-prime/b-300-crit-chance-300-strength-riding-merulina/

Surging blades :
https://overframe.gg/build/856421/yareli-prime/d-surging-blades-450-strength/

Invisible Evade Yareli :
https://overframe.gg/build/856421/yareli-prime/d-surging-blades-450-strength/

Build:

Growing power you and allies gain +25% ability strength on status effect from your weapons. So butter up that status chance!

Primed sure footed 100% knock back immunity. Currently (as of making this guide) you can still get knocked back with [Loyal Merulina] on, and I don't know if it's on purpose, but it's nice to stay on my feet, not my ass.

blind rage +99% ability strength. -55% ability efficiency.

Primed continuity +55% Ability duration.

Narrowminded +99% Ability duration. -55% ability range.

Equilibrium you gain +110% energy on health pickups and +110% health on energy pickups.

augur secrets +24% ability strength. And 40% of the energy spent you turn into overshields.

overextended +90% ability range. -60% ability strength. You can swap this for Stretch So you gain the 60% ability strength and loose -45% range from overextended that is a comfort choice.

loyal merulina you get a water puppy that casts sea snares every 3.1s (in this build, base is 2s) along with 90% DMG reduction and stagger immunity

umbral intensify +44% ability strength. +11% tau resistance.

Arcanes, Archon shards, Secondary weapon + arcane, and Subsume

Arcane Precision On headshot: +300% DMG for 18s on secondary weapon.

Molt augmented On kill +60% ability strength when you've killed 250 enemies.
Math: 0.24 x 250

Shards:

1 Tau Amber (yellow) +37.5% casting speed
2 Tau Azure (blue) +75% energy capacity x2
2 Tau Crimson (red) +15% ability strength x2

Secondary:
My choice:
https://overframe.gg/build/856721/

Secondary Arcane:
Cascadia overcharge While overshields are active +300% crit chance (add that with [Yareli]'s passive +200% after moving for 1.5s)

Subsume:
pillage remove a percentage of enemies armor and shields from enemies; all the while replenishing your shields and removing stagger from you and your teammates in range of you. (STRIP DOWN THOSE ENEMIES!)

Make Ordis happy and "Return -covered in blood- safe and sound"

About [Yareli]:

Sea snares 1st;

Sea snares apply damage vulnerability to enemies and lifts them up for easy headshots, essentially stunning them. But that damage vulnerability can scale extremely well with ability strength.

So yeah. It literally multiplies the damage the target receives! And applies to all weapon types you use

Sea snares apply cold status and if you want to run Flow on her, i recommend Archon Flow simply because you'd trigger the cold via sea snares.

Merulina 2nd;

When casted without Loyal Merulina, Merulina will act as a k-drive and provide 90% DMG reduction and stagger immunity, while on top of Merulina you'll be forced to only used secondary weapons.

Invulnerable: when you've casted Merulina you'll gain 4 seconds of invulnerability, in which DMG you take meanwhile with be added to Merulina's health. If you remove Merulina, or she died, you'll gain 1.5 seconds of invulnerability.
This means you have 5.5s of invulnerability, if you then add rolling guard that's another 3 seconds added to it.
So yes, timed right, you can permanently be invulnerable.

Merulina Guardian works well with Arcane Avenger and Combat Discipline as when taking DMG Meulina's augment heals Merulina for 20% using sea snares and can proc Archon intensify.
you also gain +200% Reload and +200% fire rate for secondary weapons for 20s which is affected by ability duration.

Loyal Merulina you no longer ride Merulina, you have her following you around like a water puppy and casts 1 Sea snares per cast on nearby enemies with a 2s cooldown. (Where [Yareli] herself casts 5 per cast.)
The cooldown is affected by ability efficiency inversely: so increasing your efficiency will reduce the cooldown to a minimum of 0.5s (at 175% efficiency)

You still receive your damage 90% reduction and status immunity as if you were riding her.
[Loyal Merulina] and your sea snares can also stack meaning you can get over 500% vulnerability damage.

Bottom line you can be and move like any other frame, you get 2 instances of sea snares from merulina and your yareli, you get semi-status immunity and you can cast subsumed abilities; where you weren't normally able to on merulina.

Aquablades 3rd:

Create a trio of orbiting blades that applies A LOT of slash procs. Essentially a cast and forget ability.

Surging blades you can throw a single aqua blade out in a straight line. The aqua blades will gain 10% DMG every time a thrown or orbiting blade hits an enemy. And while riding merulina it will not cost you anything to throw.

Riptide 4th:

Cast a water cyclone that will pull enemies in, the suction range will reduce from 15m to 5m over 2 seconds.
All enemies will receive cold damage and when you manually detonate it, it will expire and the cyclone will burst outward and apply cold DMG that is increased by 50% for each enemy still alive within the riptide.

This is affected by ability strength.

Tips:

Casting Sea snares on Merulina casts it faster. But as a single hand cast it is pretty fast already, but a casting speed shard doesn't hurt.
You also Cannot cast subsumed abilities on Merulina, you'd have to hop off and then back on.