Thanks!

That trapezoid-faced dude with the gear feels like he's just begging to have an indie puzzle platformer made about him.

I'm pretty sure that's a knight piece. It looks like a horse.

This was more or less done by none other than Alexei Pajitnov of Tetris fame — https://www.old-games.com/download/3676/knight-moves

That sounds like a great concept for an indie puzzle platformer!

The inverted triangle piece reminds me of the Lewis Chessmen.

https://en.m.wikipedia.org/wiki/Lewis_chessmen