Piloswine learns Ancientpower at level 1. This means that you have to use the Move Relearner to teach Piloswine Ancientpower. The move relearner is in the following places (note that you need to give 1 Heart Scale in all games):
Diamond/Pearl/Platinum- Pastoria City
HeartGold/SoulSilver- Blackthorn City
Black/White- Mistralton City
I haven't included previous games because;
Note: Piloswine can also learn Ancientpower by move tutor and by egg move.
Have Piloswine learn AncientPower and level it up. (Piloswine cannot learn AncientPower through level up. Go to the Move Maniac in Blackthorn City and have a Heart Scale. Talk to him and teach your Piloswine AncientPower.)
Piloswine evolves when it levels up while knowing Ancientpower.
In Generation III, Piloswine can only learn Ancientpower through breeding with a father of Diglett, Dugtrio, Wooper, Quagsire, Dunsparce, Phanpy, Donphan, Mawile, Numel, Camerupt or Kecleon knowing Ancientpower with a female Piloswine. However, a Piloswine cannot evolve into a Mamoswine in Generation III, as Mamoswine is a Generation IV Pokemon.In Generation IV, Piloswine learns Ancientpower once it has evolved from Swinub.
Make sure you have a Heart Scale. Go to the move relearner and when he tells you which Pokemon to choose choose piloswine. Then Select Ancientpower.
Piloswine evolves into Mamoswine when he learns AncientPower, sometime after Level 33.
teach Piloswine AncientPower and level it up
Piloswine evolves into Mamoswine if leveled up knowing AncientPower
First evolve it into Piloswine then level Piloswine up with Ancientpower as one of its moves
Piloswine evolves into Mamoswine by learning AncientPower. Your Piloswine can remember AncientPower(since it's a Lv. 1 move) by going to the Move Family's House in Mistralton City, and giving a Heart Scale to the reminder girl. Then, level up Piloswine while it knows AncientPower.
teach piloswine ancientpower and level it up
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In Pokémon Pearl, Piloswine doesn't learn Ancientpower through gaining more levels, it learns it via the Move Relearner in Pastoria City.