Replacing Man-At-Arms' mace with a foam rubber duplicate.

Meka-neck peeping through more windows than usual.

Call INS on Orko.

Send a love letter to Evil Lyn from Ram-Man.

Give Trap Jaw Tetanus.

Tell Merman that he's invited on a talk show for being the coolest Evil guy, and watch him get all excited.

Tamper with Teela's home pregnancy test.

Crap on the rug, and blame it on Beast Man.

Replace Moss Man's Miracle-Gro with herbicide.

Call up Mer Man claiming to be The Little Mermaid and ask him on a date. When he shows up at the restaurant, punch him in the face.

Repaint sign out front of Castle Grayskull so it reads "Asstle Gayskull."

Superglue a sword of power on the sidewalk near Skeletor's house. When he tries to pick it up, punch him in the face.

Kill Orko. Not really a prank, technically, but we'd all love to see it happen.