GrandMasterJack Casino runs a Mystery Box promotion from Monday 00:00 GMT to Thursday 23:59 GMT. A minimum deposit of £20 with code MBOX earns one Mystery Box minigame.
The box awards 25 to 100 free spins at random. The spins work on slots. It's a 50xB wagering requirement; the bonus can be redeemed once per day.
That's the whole mechanic. The offer ends on 2026-10-29 and is open to all players. You'll need the code to claim it.
