Braviary used sky drop on Gastrodon.
Both Braviary and Gastrodon would be unable to do anything else.
Braviary's partner used surf. Gastrodon's partner is hit.
Braviary drops Gastrodon and deals damage.
Gastrodon's partner hits all pokemon with surf.
So basically what I'm telling you is that when the two pokemon being lifted by Sky drop, they are invenerable to any move(except for Gust, Thunder, Twister, Sky Uppercut, Hurricane, Smack Down, and any move used by a pokemon that has No Guard)