Successfully complete the indicated stage to unlock the corresponding bonus:

Claude Lobster: Stage 4 
Flippers: Stage 4 
Flower Power: Stage 6 
Jimmy Lightning: Stage 1 
Kat Tut: Stage 2 
Multiball: Stage 1 
Pyramid: Stage 2 
Renfield Pumpkin: Stage 5 
Space Blast: Stage 3 
Splork Sporkan: Stage 3 
Spooky Ball: Stage 5 
Tula Sunflower: Stage 6