Yes, the Exotic sword. It can shoot out projectiles with its power attack that are one-shot kills and are highly accurate and can strike at very long distances. If I meet the invader right after they spawn I win the fight probably 99% of the time because I can destroy them at a distance or overwhelm them up close. Black Talon is also surprisingly good while invading too.
I combine Black Talon with a glaive and a pulse rifle and I'm good to go in Gambit.
If you're going to play Gambit I suggest giving this load-out a try. It covers the bases for all the enemies you're going to encounter.
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Favorite heavy. Then it's leviathans breath as both invader and counter