Complete any of the following tasks to unlock the Versus stage.

Defeat a zone's Boss (stage 10).
Earn an "A" rank in an entire zone.
Plant 7,000 bombs.
Destroy 4,000 soft blocks.
Get 700 packs.
Complete 300 missions.
Get 30,000 experience points.
Get a Total Best Score of over 2,500,000 points.
Get a Total Best Time of under 100 seconds.