Because Scarf Genesect is so mainstream:
Genesect @ Choice Band
EVs: 252 Atk / 4 SAtk / 252 Spd
- Ice Beam
99% of the time, you'll be spamming U-turn, and what a U-turn it is! After a Download boost, you're knocking off over half the health of a 252/252+ Eviolite Chansey, easily the strongest U-turn in the game (unless you use Swarm Scizor for some reason). For the time I've been using this thing, I rarely ever even use anything else. Ice Beam is great for the ability to check non-boosted Dragonite, Gliscor, and non-Jolly Landorus-T, and occasionally you can throw out a Flamethrower to kill off Ferrothorn or Scizor or something. I would say, however, that Explosion is probably the second most used move on this set from my experience. There are so many times where I might have Genesect out on its last leg, maybe even to the point that if I switch it out and back in, it will die to whatever hazards are left. In that case, I'll just throw out an Explosion and usually kill something once the Ghosts are gone and the resists are weakened enough. Just to put this into perspective, physically defensive Skarmory is taking 54.49% - 64.07% damage from this thing's boosted Explosion. So yeah, if you don't have a healthy resist or a Ghost, I will kill something with this thing. I have tried Zen Headbutt and Iron Head on this set, which have their uses, but usually it's a lot easier to just U-turn and bring in a counter than to try and predict a switch to Terrakion or whatever with one of the other physical moves.
TL;DR - Use CB Genesect. It's so underrated.