getting ready for a tournament and wanted to double check this, if I use a Cluster Missile am I able to use his ability twice because your are making two attacks? Card says Discard this card to perform this attack twice

Each attack granted by Cluster Missiles is distinct, the vader crew card is used after you make an attack

Q: If a ship attacks twice through some effect, such as the Gunner upgrade, can the ship use the ability of Darth Vader (the Upgrade card) twice? A: Yes, once after each attack

just wanted to double check, thanks seems kind of nasty

Well it's certainly nasty to them, but it's also incredibly nasty to you, too.

With Cluster Missiles, Gunner and Vader you can use Vader three times. No ship currently released is able to equip the combination, though.