Hey really awesome! I love games where you can summon minions to fight for you (a bit like my game jam entry also about fighting the hero!). This was really well done. I liked that there was a good variety of ally units to summon. Everything fit together really well! I won on my 3rd or 4th round, still didn't have enough to summon the Demon King though.
My one complaint is that the spike traps look a lot like a wall. When focusing on avoiding the hero or summoning units its really easy to forget about those traps, and with only 3 hearts and I believe no way to heal, it did make a couple playthroughs a bit annoying when I realized I only had 1 heart left.
Otherwise though really cool game and take on the reverse survivors genre!! Great work!!