Legion Commander + Sniper

Why this works

Catching an enemy out of position for a Duel is a lot more secure with a Sniper on your team. Legion Commander provides the long, reliable lockdown, and Sniper provides the consistent, high damage from a safe distance to make sure the target dies quickly. He can also use Shrapnel over the Duel area to slow down any potential saviors, or use Assassinate to finish the kill if the target is tough. This setup makes it much easier for Legion Commander to snowball, as there's less risk of enemy interference turning a Duel around.

The success of this pairing really depends on positioning and target selection. Legion Commander can't peel for anyone while she's in a Duel, so she has to pick fights where Sniper isn't immediately threatened. If the enemy team has multiple heroes that can jump the back line, they’ll often ignore the Duel and focus on killing the vulnerable Sniper instead. When it works, it secures important kills, but the combo falls apart if Sniper is forced out of the fight before he can contribute.