Aimee:
Complete the bowl ramp in ramp mode.

Bluebee:
Complete all 10 combo stages and the final stage in challenge mode.

Clarice:
Complete all 10 Gawoo attack stages and the final stage in challenge mode.

Grandma B:
Complete the normal ramps.

Mr. Honda:
Complete all 10 trick stages and the final stage in challenge mode.

King Gawoo:
Successfully complete street mode under the normal difficulty setting, then defeat King Gawoo in street mode (flip side) under the normal difficulty setting.