Summon Board Passive selections:
Odin choose 3 / 6 / 7
Bahamut choose 4 / 5 / 6
Usuals:
Ifrit, Shiva, Ramuh, Brothers 4 / 5 / 7
Leviathan, Pandemonium, Alexander, Diabolos 4 / 5 / 6
For more details and help with summons, check Summon Hub!
A Sphere - Yda has a BRV gain on her EX+ passive, so she benefits from spheres like Cinque or Iroha, and she's otherwise a melee attacker that debuffs with Touch of Death and likes to break.
E Sphere - S2 can occasionally debuff however she wants to use EX/LD the most so Seymour is the most consistent sphere on her.
Yda is extremely unique and most of it comes from her LD buff as it grants her access to HP+++. If an enemy is unbroken, point Yda’s HP+++ at them (provided the orb is being maintained). Breaking an enemy with HP+++ gives her a free instant turn AND queues her next turn right after (this queued turn isn’t free). It also extends her buffs, so you never need to worry about upkeeping buffs from any of her other skills. See below for infinite turns.
On her free turns you can use her other skills:
Snap Punch (S1) is best used after her HP+++, so you have the hard hitting + version. It’s a single target shave and gives her some strong generic buffs
Touch of Death (S2) is also single target, dropping her poison, sap, & hp poison onto enemies (using 2 debuff slots). This has 100% splash, so it can be good in AoE situations provided that Snap Punch+ isn’t capping. Also good if she’s being targeted as there’s a big BRV gain afterward.
Tornado Kick (EX) is just hard hitting AoE BRV + single target HP with splashes on each HP attack.
Six-Sided Star (LD) is the star of the show! A whopping 12 AoE HP attacks paired with Yda's BT effect giving her 150% HP DMG Limit leads to DEVASTATING results! Note that it will send her turn back due to it's low turn rate, but you can over come this weakness with Lunafreya or CRAB 3 (Crystal Ability 3 - Speed).
Our Final Heaven (BT) provides the party with the usual BT effects however Yda gets high personal buffs form it most importantly 150% HP DMG Limit after she's taken 2 turns!
BT Phase without U4: S2 -> LD -> S1 -> S1 -> EX -> FR
Needing to use LD early (for the free skill) is why her BT phase is not great.
Pax Phoenice (FR) is where the year's animation budget went and asks for:
Melee ability on turn: +40%
Attacking a broken target: +40%
50% HP DMG & Limit aura vs a broken target. Great FR for melee units!
With enough FR HP DMG Bonus and HP DMG Limit granted to Yda, S2 can nuke non-target enemies out of orbit in 1 go. This is due to an overflow bug and how splash works so also note you may heal the non-target enemies back to full HP. Cloud and Zack BT Finishers are another example of other attacks that can trigger the same effect.
In a realistic scenario of Enna Kros + Support BT user, Yda and Snow can achieve higher damage peaks than Astos can.
This is mostly possible thanks to Enna Kros' BT rounding, without it it is not possible. Other pieces needed are:
Ifrit Lv 50 Summon Phase (+ a buff slot for Hellfire)
The best way to concentrate this damage is with Lunafreya's Quick Prayer or Crystal Ability 3 - Speed. Note Snow loses buff application grace period and will get 1 less turn than Yda with Quick Prayer.
If you've heard of Ydaroth or wondered how Yda achieves low turn count clears, on top of her infinite turns, there is an interaction that allows her consecutive turns from HP+++ to both not count for turn count. What you'll need:
Yda EX+ 3/3 & Yda LD
Sephiroth BT (base is enough)
Kain, Freya, Cissnei, Exdeath, Yang, Vayne, etc. (basically any linked attacker who aren't Cor, Weiss or Cod that will take Yda's breaks/turns
3 calls to handle the fight's mechanics whether its for surviving threshold/force attacks or to enable damage a bit more
If you have the pieces and the fight allows for it, congrats! You can Ydaroth it.
Use Sephiroth's call then he needs to BT and have his BT effect up.
Setup whichever linked attacker listed above (use call, use appropriate BT+, LD, etc. unless you want 14 hour runs I guess)
With C90 Yda gets her LD buff right away so you can BRV++, then it's HP+++ all the way down (Yes you can just press the normal Auto button, NOT AUTO+).
Make sure your phone has enough battery and stays awake.