Bloodseeker + Night Stalker

Why this works

Hunting someone down during the first night cycle becomes incredibly effective with this pair. Night Stalker creates the perfect environment with Darkness, reducing enemy vision and making it easy to isolate a target. Once an opponent takes damage, Bloodseeker's Thirst kicks in, giving him vision and a massive speed boost to join the gank from anywhere on the map. They both excel at chasing, and Night Stalker's ability to initiate a fight and get a hero low is exactly what Bloodseeker needs to activate his passive and snowball.

This duo puts the enemy team on the back foot for the entire game. They can't farm lanes safely or move between towers without risking a coordinated gank from two of the fastest heroes on the map. Spreading out is a death sentence, but grouping up doesn't solve the problem either, as Bloodseeker can use Rupture to lock down a key target while Night Stalker silences another. The constant pressure forces mistakes and makes it extremely difficult for the other team to execute their own strategy.