I'm trying to learn this category but I'm not sure how the warp glitch works. Is there a guide/tutorial out there that I could study?

it is a weird trick but the comment that I used to learn was

"The trick is basically to do the spell input the very frame you enter the screen transition (I dunno if it's actually frame-perfect, but it is fairly specific). The way I input it, is by doing most of the half circle before I push the jump button, so when I'm mid-air, I basically only have to time up -> attack for the transition. To put it short, down -> right -> jump -> up -> attack."

What's the proper way to enter this room?

nvm got it
thanks for the tips!

No problem. I'm learning this as well. I have tried to finish an Any% run at AGDQ2016 for like 8hrs. Couldn't complete it. Dracula is a jerk

Are there any tutorials for this game? Any categories?

Here's a link to the Vampire Killer All Bosses tutorial video. I've also updated the links to the guides so they aren't broken.