My team:

Golem: Final Rock/Ground
Psyduck: Basic Water
Sandshrew: Basic Ground

Psyduck versus Cubone: Water is Supereffective against Ground, Cubone loses.

Sandshrew versus Geodude: Ground is supereffective against Rock (funnily enough Ground is one of the few types which doesn't resist itself last I checked), Geodude loses.

Golem versus Onix: They're both exactly the same mechanically, so it's a draw.

End Result: V I C T O R Y !