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All bets are off
pit fighter attack 11

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

Hit: 1d6 + Strength modifier damage, and the target is dazed until the end of the user's next turn.

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.