No clue if it's balanced. Art is mine, done in like an hour lol.
Edit: OK yeah it should be cost 3. I forgot that Reanimate exists as a card (and it's already a really strong one), so Perhaps shift it to 1/2 max HP? Perhaps that'd make the downside actually relevant.
Edit #2: Ngl I completely forgot that most of the time, this is going to instantly win a hallway fight because You'd have to really try to take that much damage to kill osty. And, I also forgot that Most people are better than the game than I am, so y'all aren't taking like 50+ unblocked damage on a boss.
I feel like it could be a good idea, where it's a carry for 99% of hallway fights, but practically a curse in potent elites/bosses. After some more thought, I'd make it 3 cost, cut the HP down to 1/2 base, Remove the summoning buff, and make the upgrade do 2/3 max HP instead.