Mythic Valk AI is nothing if you one-shot her. <3
Shotted Zeus with Goemon + Ur + Freyr, so I figured I'd try the same thing for Valk, since she has less HP than Zeus. First two floors of Legend and Mythic are exactly the same, so with a little luck from no heart cascades in the later floors, a Goemon team can do Mythic Valk same as Zeus.
Cost 2 stones for being retarded, but 1 was going to be necessary from bad boards. 0's possible with a little luck. But that's not bad for 100% drop. Valk #2 get.
Team used: Goemon, Freyr, Horus, Gigas, Siren
I still need to clear Legend for the dungeon clear stone, but I don't want to spend any stones to get 1 back... not sure how I'm going to gameplan for Legend yet.