Shadow Shaman + Io

Why this works

Seeing an enemy Io Relocate into your lane is always a threat, but seeing it bring a Shadow Shaman is a special kind of problem. The instant disable from Hex means a full duration Shackles is almost guaranteed, locking down a single target for an incredibly long time. Io’s Tether ensures Shadow Shaman has the movement speed to stay on target and the healing to survive if the gank gets turned around. It makes picking off isolated heroes much more reliable, turning what might be a risky play for a lone support into a nearly certain kill.

This pressure forces the enemy team to play differently. They either have to group up earlier than they'd like, surrendering farm on parts of the map, or they have to spend a lot of gold on vision to try and spot the Relocate ganks before they happen. While the duo can create a strong mid-game advantage by picking off cores, the strategy relies on finding those single targets. In full five-on-five teamfights later on, this specific ganking synergy matters less, which is why it's a helpful pairing but not a completely game-defining one.