Crystal Maiden + Lifestealer

Why this works

Trying to kite a Lifestealer becomes nearly impossible with a Crystal Maiden on his team. Lifestealer has the damage and the slow from Open Wounds, but he lacks a reliable way to lock a target down. Crystal Maiden provides exactly that with both Frostbite and Crystal Nova. A single root is often enough for Lifestealer to close the gap and stick to a target permanently. The global mana regeneration from Arcane Aura is also a huge help, letting Lifestealer use Rage more freely to stay aggressive or escape ganks without having to worry about his mana pool.

This duo comes online early and defines the mid-game tempo. A successful gank usually turns into a tower or a Roshan attempt, as opponents are forced to respect the pick-off threat. To play against this, you need to either split them up by focusing the Crystal Maiden first or buy items like Force Staff and Ghost Scepter to survive the initial lockdown. If Lifestealer gets ahead, he can even Infest his support for a surprise initiation, making it incredibly difficult to feel safe anywhere on the map.