Since I started attempting 100% runs I've discovered some glitches that I think you should know about.

Bothways Walk (i know it's a dumb name idc)

If you hold both left and right arrow keys/buttons you'll stand in place, but the animation will look like you're walking to the right. Which on its own is... completely useless!

Bothways Walk Dash (nice this one's even worse)

If you dash while performing a bothways walk you'll dash to the right without actually moving. This can be used to make killing zombies and slimes less of a run-killer for 100%, since enemies can't kill you if you don't collide with them, but can die from the dash if they're close enough to your right.

Snow Bothways Walk Dash

If you do the bothways walk on snow you'll start constantly switching between facing left and right, unlike with normal bothways walk. Combined with dashing that obliterates any zombie around you with no risk.

Glitchy Arrows

Arrows in this game are indeed glitchy. You can sometimes dash or even walk right through them! This can probably be exploited if we can figure out the reason behind this glitchiness which requires dedication and knowledge of PICO-8's programming language, which I lack, unfortunately. If you're trying to research this, hit me up on Discord, I'd love to help.

Trap Block

After collecting the diamond gem don't jump back up the hole that you've fallen out of. The lowest block of the ledge that supports the lower group of spikes is broken. You can jump inside of it and you can't get out, you're just gonna be stuck there until you reset the cart.