In a DVD review of SpongeBob SquarePants: Season 4 Volume 2 at DVD Talk, the final two episodes of season four are revealed. They are "Hocus Pocus" and "The Thing" (both available on disc two of the DVD). Here are the summaries for the episodes.
Hocus Pocus: SpongeBob tries out his new magic kit on Squidward and is convinced he's turned his neighbor into an ice cream cone!
The Thing: After a freak bicycling accident, Squidward is coated in so much gunk, he's totally unrecognizable. SpongeBob thinks he's cute and adopts him as a pet.