Notes & adjustments:
Turn 1: Penth s2, Arash s3 then np
Turn 2: Waver s2 + s3, Penth s1 + s3, Mordred NP (assassin will survive with 15 - 20k HP but should die just fine with any next 2 cards)
Turn 3: Mordred s1 + s2 + s3, Waver s1 on Mordred, swap Waver with Merlin, Merlin s1 + s3 on Mordred, plugsuit atk, select the ruler/avenger. Mordred NP + Penth NP + any card (preferably a buster)
* Penth's skills can be upgrade further (e.g. 9/6/9 or 10/6/10)
** Merlin's S3 can be placed on Penth but I encountered some runs where the archer lives with around 4 - 5k HP after doing the Turn 3 chain (extending the run to 4 turns). Putting it on Mordred should/will ensure killing all the other mobs leaving only the ruler/avenger for Penth's NP + 1 card