Which Platformer with characters stacking on one another is found in this Jimquisition Video?

The game is called Lapis x Labyrinth.

While I linked the switch page, it is also available for PS4

I've found it by pausing the video on a frame with two enemies defeated messages, and googled both of them ("Hammer knight" "Killer bee")

After a long time scrolling through the comments on that video, I finally found the answer.

It is Lapis x Labyrinth for the Nintendo Switch. It is made by Nippon Ichi Software, Inc. and releases tomorrow, May 28 2019 (May 31 2019 in the EU).

Here's a trailer for it:

Since you're already on Jim's channel, here's his review of the game: