A tile on a timer. Load it up with 6 balls, which dwindle over the turns, and eventually self-destructs. You can even add to the timer count if a ball manages to jump into it. The tile allows for regular balls too. Figured I'd clarify considering the pictures and rules.

Rules Setup: Must contain 6 balls (alternative balls allowed). Ongoing: On rolls and spawns, use a ball from inside this. When empty, destroy this. Forbidden: Balls inside don't count towards 3-Ball rule. Note: If playing with any alt-balls and the open version... The active player decides which alt-balls go into this during setup.

Alternative Balls If you are interested in the alt-balls, check out my Converter tile as I go into depth there.