I do have to admit that I love exploring all the dungeons in this game--and ice caves are a kind of guilty pleasure of mine. Of course they all end up having that one predictable sliding-on-the-ice minigame, but I actually like that one (see also: Conveyer Belt minigame. But fuck you, teleporter game).
The reason I was rerouted into the Frost Cavern is because the only other way East is through a snowy path in the mountains that can only be crossed by riding on the back of a Mamoswine. Very Cool. Apparently the Mamoswine in question was feeling down in the dumps and the only way I could make him feel better was to go through the Frost Cavern. Very Uncool.
Frost Cavern was full of interesting Ice pokemon, including a new pokemon called Bergmite whom I caught easily--and at the end, the big revelation was that Team Flare was behind the whole mess! >GASP<
Apparently Team Flare was picking on a resident Abomasnow (most likely for being a stupid Sesame Street muppet) and I had to fight them off to make the Abomasnow feel better--and therefore to make the Mamoswine feel better.
After I made the Abomasnow feel better, it gave me "Abomasnowite" (which I assume mega-evolves Abomasnow) and I made my way East on the back of a Mamoswine. Along the way, "Scrappy" the Scraggy evolved into "Scrappy" the Scrafty.
On Rotation: Gardevoir, Pikachu, Lucario, Skrelp