[ti]Insane[/ti]Tria. Collab

I'm new here, and want to do some type of collab. I see many of them around, but don't know exactly how they're done. I already started working on a level called TriaDot, (YouTube link attached) and am in some sort of Creator's Block, so I want to turn it into a collab with one or two people (not one of those weird mega-collabs). Could someone explain how these collabs work so I can make one with someone, and if you're interested, post here. Thanks.

YT Video: www.youtube.com/watch?v=LgGso_nRCdg

Btw the last part with the Rainbows isn't that good and might be changed.