Since people can't be original (sans a few of you) I decided to moreorless just throw starting points for each boss (except world 9) and replace/update them with better ideas if we get any:
World 1 Castle: Mecha-Tree
World 2 Castle: Pirangler*
World 3 Castle:
World 4a Castle: Jelectro**
World 4b Castle: Desert Cat
World 5 Castle: Balloon Animal*
World 6 Castle: Blimp Duck
World 7 Castle: Fire/Ice... thing
World 8 Castle: Doc Croc
Final Castle: Norveg
World 9:
*Claimed
**Completed
World 1 Castle: Mecha-Tree
World 2 Castle: Pirangler*
World 3 Castle:
World 4a Castle: Jelectro**
World 4b Castle: Desert Cat
World 5 Castle: Balloon Animal*
World 6 Castle: Blimp Duck
World 7 Castle: Fire/Ice... thing
World 8 Castle: Doc Croc
Final Castle: Norveg
World 9:
*Claimed
**Completed