To switch game mode from Chess to Drafts (Checkers).
This could only be used twice per player per game, in unrated games only. The toggle is valid for the duration of one move, and allows the player to use one counter to take as many pieces as possible according to the rules of drafts (checkers).
It should be available twice per game, as this would allow once go on White diagonals, then another on Black. A validation rule must be built into the design to ensure players adhere to this special rule.
Careful use of this option could lead to spectacular changes in the game position - with often hilarious results.