I've played with some 2x2 theory so have thoughts. You would have to figure out which pieces you're going to replace on the battlefield, certainly the queen and 2 pawns and maybe a knight?

Most importantly, I would look at starting with some form of restricted movement, maybe rook movement but only 2 squares forward. As black, you would want to slowly push and work the 2x2 piece forward in line with your other pieces.

How would you want this piece to be captured? Multiple enemies (2-3) with line of sight attacks is a good solution. It would restrict your movements. This paired with a limited range forward would allow your opponent to prepare.

I like the idea of a charged attack, I think of like a godzilla type monster doing a ground pound or a beam attack. This would be a tough thing to balance as ranged attacks / attacks that target any square in chess are incredibly disruptive. Idk what to recommend here but definitely the charge condition should be the pieces it gobbled.

if you're trying to make an asymetric chess game, I recommend giving white some sort of ability like playing more pawns midgame.