Regigigas needs a lot of things, but Shell Smash is not one of them. It doesn't even make sense that it would get that move.
Mew lacks wings and empoleon lacks claws, but they learn Steel Wing and Hone Claws respectively. And Shell Smash would negate the effects of Slow Start entirely, and may get him to at least RU. Trust me, I owned in balanced hackmons with a Shell Smash Regigigas before. --- Mentions of Zangoose since 6/27/2013: 1 Official Shadow Zangoose of the X board!
Empoleon has claws. What do you think those sharp things on the inner parts of its flippers are? --- "Murder of the living is tragic, but murder of the idea is unforgivable." - Janus, speaker of the synod
I'm always the first to say "It's a video game. Don't worry about logic." when it comes to Pokemon, but giving Regigigas Shell Smash goes beyond that. There's being illogical, then there's being crazy. You crazy. --- THAT'S MISS FUNERAL CAKE TO YOU why you be hatin', mosquito?