Boss Idea - Elemental - 4 stages

I was thinking of a way to do a multi-stage boss and thought an "Elemental Boss" could be fairly straight forward. Elemental in German translated as "natürlich" which is rad, because NATURE and LICH, hell yeah. His main character card can be split in two on both sides, with STAGES 1-4 represented by the different elements. He starts at STAGE 1 in Wind form. After the heroes defeat that stage, the card is rotated to STAGE 2 - Water. STAGE 3 will be on the backside of the card, Earth. Then rotate that for the final form, STAGE 4 - Fire. The different stages/forms of the boss would have different hit points. There could possibly also be a "resting round" in between every stage as the boss transforms, letting the heroes heal up. The other twist that could be fun for this boss and his deck of minions/spells/attacks could be: All the cards have a general effect like "Rocklings deal 5 melee damage to the character who has aggro", but then they can also have a secondary effect like "If BOSS is in Earth stage, then all characters take an additional 2 HP damage". I can imagine that the boss is just spouting out minions and havoc which could explain Rock Monsters followed immediately by Water Monsters - but then if they happen to come out at the appropriate stage, the monsters would be deadlier.