Bloodseeker + Snapfire

Why this works

Pairing these two heroes is a bet on their ultimates syncing up for easy kills. The classic combo is Bloodseeker's Rupture followed by a Firesnap Cookie from Snapfire, which forces the target to move and take a huge burst of damage. Even without the Cookie, a ruptured enemy becomes a perfect stationary target for Mortimer Kisses, as they can't run out of the impact zones without hurting themselves. Bloodseeker benefits from the slows and stuns, letting him get more attacks in on low-health enemies revealed by Thirst, while Snapfire gets easy setups for all her spells.

This plan works best during mid-game ganks where a single pick-off can open up the map. The combo isn't foolproof, though. An enemy can teleport out of Rupture, or stand and fight if they're strong enough. Both heroes' ultimates have significant cooldowns, and if they aren't available at the same time, the synergy is much weaker. Opponents will play around these timings, looking to fight when the combo is down. The advantage comes from the pressure this duo creates; enemies are forced to play more cautiously, knowing one mistake could lead to a guaranteed death.