Left facing spike clip: By changing your horizontal parity by either empty dashing (dash without giving a directional input) or walking into the right side of a wall, you can walljump off of left facing spikes. This works because your x position is always even and by changing your parity to get an odd x position you can get just barely close enough to left facing spikes to wall jump off of them.

Up facing spike clip: Spikes in Celeste wont kill you if you're moving away from them. So if your vertical velocity is negative* (you're moving away from the spikes) but its not actually high enough for you to move a pixel, you will be able to clip the spike. This is normally done by lining up the apex of your dash with the spikes

*If the negative part sounds weird, trust me there's a logical reason for it

Down facing spike clip: Nothing much to say here. If you're moving fast enough you can straight up go through the spikes. This allows you to clip the spikes at the top of 2500m and save loads of time

Right facing spike clip: Doesn't exist PogChamp

Grace jump/Coyote jump: Once madeline walks off a platform, she has 6 frames in which she can still jump.

Corner jump: While its named corner jumping and it looks like you're jumping off of the corner of the block, what you're really doing is wall jumping off of the left/right side of the wall but right after passing beneath the corner of the block. See how taseline performs 2 of these at the end of the gif.

Gem skip: By dashing the frame before the chest animation freezes madeline, you can buffer a dash that will happen once the chest animation is over, however you will regain your dash after this buffered dash allowing you to skip the gem. This works because when you hit dash you freeze for 2 frames before dashing.

Double walljump: In the words of @Juice "yeah you get height because the first one is right next to the wall so you stay close enough in to get back and gain height but the second one is a bit away from the wall so you can't gain height indefinitely only once" (GIF from failed PB pace run by @Akliant917 )

Cloud boosting: The top of a cloud is a solid platform that you can walk on so if you dash up into a cloud you can regain your dash back and also quickly jump from the cloud allowing for better movement.

Berry block suction thingy mabob: In the words of @Meep_Moop "You have to be touching the block Then dashing away from the block while still touching it And it tries to bounce you in the opposite direction you're traveling in So it bounces you into the block"