Isn't Shea kind of a prospect for Legion himself? I mean, he's only caught Dark-types so far, Legion's specialty...
EDIT: So it took me awhile to realize that Regice can't learn Ice Shard in game, but hey, I heard somebody in some other RP talk about how retarded the breeding system was, so I made a small bend and gave an explanation as to how Chill could find its way beneath the ice, as no other Ice type attack explained it as well. Regirock knows Stone Edge so he can burrow beneath the earth, and Registeel knows Superpower to burrow through metallic obstacles such as steel walls and beams.