Yes. He is in Blackthorn City
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Blackthorne City, to the west of the pokemart
There is no move relearner in Crystal
if it is the same as in soul silver it should be in blackthorn city in one of the houses
You have to take him to the Move Relearner in Blackthorn City with a Heart Scale. Get him to teach Piloswine AncientPower. Once that's done, go level up Piloswine with that move and he'll evolve into Mamoswine. You can get Heart Scales by smashing boulders, but it might take a while.
Yes, go to the move relearner with a heart scale and piloswine. The first move on the list should be ancient power.