No indication that the attack is limited, but I'm 90% sure the implementation is broken. It's a nice idea but desperately needs some indicator that it's going to happen - simply dying because you tried to kill a monster but the attack decided to not work is not fun.

I never managed to kill anything. The attack only worked for me at the start, then it never worked again. Jumping (without attacking) disabled all future attacks. Clicking the window ... disabled all future attacks. Standing within 6 feet of any monster was randomly 50/50 instant death.  I gave up after about 15 attempts to get past the first monster :(. I don't know if I was doing something wrong.

I beat the game. The art and animation are pretty solid, clean and fit theme well. The tileset is a little sparsely used. The jump mechanics were a bit rough, very Castlevania, fixed width jumps with no air control which made for a very punishing platformer. The biggest flaw in the game were the enemy hitboxes, they were really quite large I'd often get hit by enemies above me or who hadn't yet touched me. I think the sword mechanic is cool but I don't think death after the last use is a good approach, I think it would be better if you gave an indicator and let the player try to make the rest of the level without it. Music and sound were cool but I wished there was a little more sound and that the music didn't start fresh each level as the few times I let it play it got pretty cool. It is a really lovely game and the visuals show a lot of care.