War's Wager

This golden axe is enchanted with haphazard divination magic. Its split blade features a spade, club, heart, and diamond on each of its four faces. You gain a +1 bonus to attack and damage rolls made with this magic weapon. When you hit a target with this weapon, you can choose to roll a second d20 before calculating the weapon's damage. If you roll an 11 or higher on the second d20, the blade magically seeks out and hits the weakest point of the target, turning the attack into a critical hit. On a roll of 10 or lower, the blade ricochets harmlessly off the original target and scores a critical hit against you, instead. When the axe hits you in this way, its damage ignores resistances and immunity.