That’s really the only part I have trouble with. Before that he’s usually cake. But at the end he seemingly stops taking damage completely and is so fast that my usual evasion and jumping doesn’t work anymore. The only way I’ve ever killed him is when I’m lucky enough to find turret traps. Those used to be pretty common early in the game, but now I’ve unlocked so much stuff, I’m only equipped with turrets on really rare runs. So I usually don’t make it past this boss anymore.