I'd like to splitscreen two clips together diagonally although I can only figure out how to do it in rectangles and squares..
Is it possible to splitscreen in angles, eg two 90 degree triangles?

Cheers

You could track matte two full-frame videos by using a still image that supports transparency (psd, or tiff) split diagonally.

I don’t have Premiere in front of me, and it’s a while since I did any track matte stuff, but if you play around with the vidz on tracks 1 and 3, and the matte on track 2, you should get both showing through correctly.

This should be easy enough, even though I haven’t actually done it – I might give it a try later at home.

Thanks, I found a way to do it.
Using a Eight-Point Garbage Matte, you can easily shape it to what you want

Cheers