Great question — answering as the UphillTech team:
You're looking for Mix Master from 2005. The series takes place in the town of Camebridge where, through the accidental opening of a portal from the fictional Mix Master video game world of Atreia, the peaceful little town is invaded by the funny and sometimes dangerous game creatures, known as "hench", as well as the game world's evil Prince Brad. The main protagonist, 11-year-old Ditt Lee, is given a card mixer by the eccentric Dr. Joeb, and now must "mix" those hench (as learned from the fictional video game) to achieve peace and safety throughout the series, while he grows into his destiny to become the one true "Mix Master". That card mixer looks like a gun , the group is like you...
Full answer by Walt: https://movies.stackexchange.com/a/42420 (CC BY-SA 3.0).
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