Blackjack where you may swap the second cards of your two hands.
You get two equal hands and may swap their second cards, in exchange for a dealer 22 being a push and blackjack paying 1 to 1. Example: with 10-6 and 5-A, you can swap to 10-A (21) and 5-6 (11). Decide the switch by the pairing whose two hands add up to the higher EV (expected value); an ace and a 10-point card made by switching is a plain 21, not blackjack. An unswitched blackjack still beats a dealer 22, and under the published standard rules (6 decks, H17, dealer peeks) the house edge is 0.58%.