In white 2
You do need to teach it via TM to any of its compatable parents(male) in GenIV. Then you have to breed it onto a Mudkip. OOOOOooor, you can just teach Swampert Ice Punch via Move Tutor in Black2/White2. And Ice punch is better anyways.
Breed it with a male Lapras/Mudkip/Marstomp/Swampert/Snover/Abomasnow
Source : http://pokemondb.net/pokedex/swampert/egg#move-avalanche
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