Bristleback + Broodmother

Why this works

Thinking you can focus down one of these cores is often a mistake. Trying to burst Bristleback means your team is clumping up for Quill Spray stacks while he gets tankier. During that chaos, Broodmother and her spider army are free to push down a lane uncontested. If you decide to go on Broodmother instead, you're fighting in her webs while Bristleback runs at your supports from the side. Both heroes demand a specific kind of attention from the enemy, and having them on the same team can stretch an opponent's resources and focus thin.

This pressure isn't always active in the early game, but it becomes a problem for opponents during the mid-game. Broodmother establishes her own area of the map that is dangerous to enter, forcing responses. This frees up Bristleback to group with the rest of his team and force fights or objectives elsewhere, knowing the enemy can't commit their full team to stop him. It creates a constant split-pressure that can overwhelm uncoordinated teams, though it relies on both cores having a good start and the enemy lacking easy answers to either hero.