I definitely forgot at least a few major things, but here's this:

CLIPS:

• ceiling clip. go to a ceiling as a slime, switch forms to hero, jump, and wow you clipped. You can also do this but with a spider if you go to a corner.
• wall clip. Very similar to ceiling clip, except you do it at a wall, and it's quite a bit more precise. Just jump at a wall as hero, then double jump, and swap to spider (make sure to hold towards the wall)
• Object clip. It's usually done with crates, though it works using most other objects as well. Get the object next to a wall, stand slightly away from the wall, and then punch. You should go through the wall.
• Ground pound clip (GPC). ground pound as a human, and change forms into slime just before hitting the ground. (this is technically doable without the ground pound, but much harder)
• Mole clip. Move into a mole (the ones that throw dynamite) while it's underground, from the side, as a slime. Once it comes back up, jump. You should go underground.
• Spaceship clip. When there's an enemy next to a wall in a space segment, you can clip through said wall by being between the enemy and the wall during invulnerability. Useful in the 2 space levels because there's an oob color jar.
• Boxes. They can clip you underground or through walls if you do it right. Or if you do it wrong they clip themselves underground or through walls.

HEIGHT GLITCHES:

• Infinite height. You can keep swapping between slime/spider and hero to gain height infinitely. Most people ground pound to give a larger window, but I don't think that's a great idea with ground pound storage existing.
• Spider jump. If you jump as hero (or slime), then swap to spider asap, you can get some great height.
• Ultra jump. I have no clue how this works. It's like a spider jump, but you get roughly 5 times the height. It seems more consistent at the top of ramps, though that probably has nothing to do with it. Almost definitely frame perfect. It can also occasionally clip through any ceilings above you as well.
• Dog jump. I don't know if I'd call this a "glitch", but it's noteworthy enough. Press jump at the same time as you land on an enemy to jump quite a bit higher than normal.

OTHER RANDOM THINGS:

• Ground pound storage. Only works with the slime. While you're in the air from ground pounding as a slime, swap to a different form. Whenever you want, you can swap back to slime and finish the ground pound. However, this ground pound is a bit different, in that you can still jump or move from left to right while in the air.
• Punch storage. Works the same way as ground pound storage, but for hero form, and punching. Once you re-release this punch, your downward momentum doesn't reset, but you do get the horizontal boost from normally punching.
• Punch Storage Part II: first off, you can preform PS with a ground pound. While your punch is stored (with either GP or transformation), its hitbox will continue moving, punching everything in its way. it won't be stopped by anything, including walls. it also can't interact with anything beyond punching. GP PS ends when you hit enemies that bounce you back on hit or when the the ground pound ends. Transformation PS ends only when you swap back to human. If transformation ps is done on the marshmallow ghost (ameba?), then the game will crash shortly after the second hit.
• Box man. Get a box onto a steeper slope, and then run down the slope. You should go inside the box. There's a few other ways to trigger this, but that's the easiest. If you get a spider into a box, you can "fly" up a bit by holding up.
• Slime under water. right as you touch the surface of water with slime, press R. (at least, I believe that's how it was done) Maybe possible with spider? Being a slime under water is actually painfully slow, so this is mostly useless
• Physics. ceiling corners can send you down very quickly, and you can punch to get bonus height for no real reason. This game's physics are a bit strange, I suggest you mess with it.
• Death Softlock. If you swap your weapon the frame you die, the game softlocks.
• Anti-Spider Form Swap Crash. If you swap your form in the middle of the anti-spider hallway in drip drop docks or toggle tower, your game can crash. It's much more consistent in toggle tower, however. (probably just has to do with the sheer number of loaded objects, due to the spider repellent)
• Pause Storage thing: if you pause the frame after starting a room transition, the game will remain "paused". Pausing the game again in this state crashes the game

RANDOM TIDBITS ABOUT RESETTING:

• If you reset during the questionnaire or during the cinematic after that, you go back to the questionnaire.
• If you reset at any point between right after the cinematic and when you first gain control of your character, the game will put you where you were in the cutscene.
• Afterwards, if you reset, you'll be put at where the game last saved (whether the save indicator popped up or not)
• If you reset after drawing something, then your drawing will save and be put in the creation hall. Objects will still be interactable, but weapons will be inaccessible.
• You can reset after drawing the first weapon from isaac to save the drawing, and then do that again and then go through with the last weapon to technically draw all three weapons without paying. however, you only get to use one.