Wondrous Item, uncommon
This bag of marbles have 1d8+1 marbles in it.
As an action, you may throw the marbles on the ground. Each marble summons one Goblin (use the Goblin stat block). If you summon more than one goblin, they share the same initiative and action in battle. The goblins are friendly to you and your allies. The goblins can be given simple commands, such as opening doors and pulling levers. The goblins lasts one hour.
After one hour, the goblins disappears.
The bag can regain marbles by putting the right eye of a goblin in the bag and shaking it. The eye then turns into a marble.