If you're doing a power-up piece, one idea I had was a piece that removes instead of adding.
There's a lot of games that have like bombs, but this game has the square 3x3 blocks, so blowing up a square area would be a little too strong.
So my first idea was it's a random L or S tetris piece (so it's consistently 4 blocks in a weird shape), and it's holes instead of blocks. No limits on where you can place it. It turns the area you place it on into empty space.
But I think that's a little too simple. Too good at cleaning up messy areas with many small holes. So maybe it's better to have a piece that replaces blocks with holes and holes with blocks. At worst you just play it somewhere with no pieces and it works like a normal piece.
An inversion piece like that should probably have very simple shapes, though. Boxes and lines. So you don't need to think super hard about how to use it.
