Lit up tiles
Each or certain turn(s) special tiles light up. When moving into this tile you get a buff, or a debuff.
Maybe static position. Maybe randomize position. Maybe a locked tile that unlocks each other turn.
So instead of fighting on a board you now fight on a board sized grid that moves up one row each turn. Exposing new creatures and that are already cast beforehand.
Use of towers in co op behind both players where sometimes a well is placed. Maybe use tower in general. Something that attacks certain tiles that either we or the opponent have to move through.
Certain boss encounters will imprison creatures in a tile they will protect with their creatures.
Keep this creature alive
While defeating Garudan you must keep this creature alive.
Danger rows or tiles