This team is based upon the Myth Heir teams, utilizing the Turn Meter boosting abilities and debuffs of Ruella along with the Cleanse, Speed buff, and Block Debuff buff of Elva Autumnborn to build an unkillable team focused around Demytha.  The advantage to using Ruella is an added DPS champion who can help with the speeds, adds a permanent (with the Demytha buff extension) Crit Rate buff and consistent and useful debuffs.  It is not full auto, needing a 2 turn delay before using Elva’s A2 skill (A1, A1, A2), but after that point will run on auto.

(all speeds are with Elva’s Aura)
Demytha – 295 (prioritize a2 first then a3)
Ruella – 294 (True speed must be faster than Demytha; prioritize the a3 first)
Elva – 244 (A1, A1, A2; 2 turn delay of the A2 skill)
Seeker – 188
DPS – 155

The listed speeds are the minimums and should be adjusted accordingly to different base speeds and champions.  There is plenty of room to adjust up on speeds, though the speeds of Demytha and Ruella are closely tied together – raise one, you’ll likely need to raise the other.  Elva is essential to remain affinity friendly, though other champions (like Heiress or Lydia) can be used in that position.  Ruella must have her A3 prioritized to maintain consistency.