General:
* Prank
* Trick
* Gag
* Stunt
* Jib
More playful:
* Mischief
* Shenanigans
* Tomfoolery
* Hijinks
More malicious:
* Hoax
* Ruse
* Ploy
* Gotcha
Informal:
* Goofy
* Goof
* Silly
The best word to use will depend on the specific situation and the tone you want to convey.