Dawnbreaker + Io

Why this works

Relocating in with Io while Dawnbreaker uses Solar Guardian on the same target creates an instant three or four-man gank anywhere on the map. The target gets hit by Dawnbreaker's landing stun and heal pulse while Io arrives to add Tether's speed and Overcharge's damage reduction. The sudden arrival of so many heroes is overwhelming and almost always secures a kill. After the initial burst, Io’s Tether helps the relatively slow Dawnbreaker stick to fleeing enemies, ensuring her hammer combos and slows connect.

This global threat completely changes how the enemy has to play the mid-game. They can't group up to push a tower or gank a core without the risk of an immediate, full-team counter-initiation. It forces them to spread out and play passively, ceding map control and objective timers. The main counterplay is to find and burst down Io before he can get Relocate off, or to have enough global presence of their own to split the map effectively. Otherwise, the Dawnbreaker and Io duo dictates the pace and location of every fight.