Wall cling by holding the stick straight left or right (not right-up, not right-down) and once you've clinged, you can keep clinging for a few seconds if you want. Clinging also gives you your double jump back. I advise double jumping with a button instead of the stick once you cling so you don't accidentally de-cling, as declinging/walljumping out of a cling are also possible.
I mainly use the cling on green hill zone or yoshi's story. It's really only useful for stalling. And I can get it to work consistently, just tapping and holding towards the stage as you move past the wall.
Only useful for stalling? Wooooow
Disagree. You can use a double jump and side-b to reach the wall and then get your double jump back when you cling, as many wall jumps as you want, aqaujet if high enough or pause and up-b when it looks like you would normally aqaujet. It basically increases you recovery's length, your recovery mix-up potential 10-fold and also boosts our offstage game. Cling is an invaluable tool for us.
(Btw, trying to "stall" for the 8 or so seconds that cling allows is just asking to get bopped on reaction by the opponents gimping move of choice.)
*edit*
I may have mistook "stalling recovery to mess up their edgeguard" with "stalling for time". Still, it's good for more than just that.