https://drive.google.com/file/d/1D49FMR-z7HSCBcRJSFj2JNnR7XXTZKyF/view?usp=share_link

In this video, I demonstrate a way to skip escorting the snowball through 4-Ex. This works because, so long as you're standing in front of a door and not too high up, you can go through the door; this means that, if you can place a keystone in front of the door and stand on it, you can get through that way.

Note that the 'ledge' under the door isn't actually a platform; the intended strat here is to escort the snowball through the level, and by the time it gets to the end it's big enough that standing on it lets you enter the door. Instead, using precise Reisen hovers and a backup peach you can place a keystone and get on it before dying to the spikes. If you can get on the keystone but you're too high on the door, you can short hop, land on the rock while it's falling, and hit [up] to enter the door.

I also tried using sloped ceiling clips; while you can clip into the ceiling and get above the door, you can only get back in bounds through a sloped ceiling, and the only ones of those are before the spikes, and collision in the region around the door seems solid. This could possibly be used to skip the back and forth sliding through the zombies, but I haven't pulled that off and timed it yet.

I'm not sure if this strat is worth using in 100%; while it's certainly much faster than escorting the snowball, it also requires bringing a Tenshi powerup, and I'm not sure if it's worth going out of your way to get one.