Assimilation

When a piece captures another, it permanently acquires its movement abilities.

In Assimilation, capturing is more than removing a piece — it's absorbing it. Whenever one of your pieces captures an enemy piece, it keeps its own movement type and permanently gains the captured piece's movement abilities too, stacking across the game. A knight that captures a bishop can then move as both a knight and a bishop for the rest of the match. Standard rules for check, checkmate, castling and promotion are otherwise unchanged.