I passed the Insane mode with next cards:
- Heal card (Holy Priestess 3750 heal when boss deal 3720 damage every turn),
- 2 hp cards (any or with +poison, useful with boss).
- 2 hit cards (any) and 50% reduction card (Pirate Lord Blackbeard).
General hp is: 11k+.
Boss: "The Death",
- Card active skill: Within 2 turns, changes 5 random non-water symbols (Free spin, wild and chest symbols excluded) into water symbols.
- Passive skill: Chances of matching water symbols get significantly increased.
I hope this info will be useful for other players! Also would be nice to see info about Hell mode)