According to this question, Genesect gets something called 'High Speed Flight Form', viewable for only a few seconds once you let it out of it's Poké Ball. What does it look like, and is it an official Forme? Other Pokémon have diferent stances when released from their Poké Ball; Metagross has his legs locked in an X position, then releases them when he lands.
It is just the way Genesect flies in the anime. It pulls its arms/legs in and flies flat. Not officially a form, as it can't be seen in the games, only anime.
That's what it looks like.
Its a flying saucer like forme Genesect uses for flying and traveling Extreme Distances Much Faster. Its mainly only Seen in his movie and anime but GF made it his Pokeball exit for Gen VI.