Target: one creature
Attack: Strength vs. AC
Hit: 2[W] + Strength modifier damage. The user then makes a secondary attack against the same target:
Secondary Attack: Strength + 2 vs. AC
All bets are off is an 11th-level pit fighter encounter attack power. On a hit, it deals damage and allows a secondary attack against the same target. The secondary attack has improved accuracy, and the target takes damage and becomes dazed on a hit.[PH:88]
The secondary attack is a melee weapon attack, despite the flavor text and lack of [W]. This has been confirmed by Wizards of the Coast.