Synonyms for Mischief:
General:
* Prank
* Trickery
* Naughty
* Rascality
* Misbehavior
* Troublemaking
* Pranks
* Tomfoolery
* Harmless fun
* Fun
* Devilment
* Waggery
More serious:
* Malice
* Viciousness
* Mischief-making
* Intrigue
More playful:
* Playfulness
* Frolic
* Horseplay
* Caper
* Roguishness
* Impishness
Informal:
* Monkey business
* Shenanigans
* Ruckus
* Hullabaloo
* Goofing off
Literary:
* Larking
* Mischief-making
* Frivolity
* Knave
* Imp
The best synonym for "mischief" will depend on the context and the specific tone you are trying to convey.