Monkey King + Primal Beast

Why this works

Drafting both of these heroes creates a team that's trying to do the same thing twice. A Primal Beast wants to be the primary front-liner, charging in with Onslaught and holding a target down with Pulverize. Monkey King also wants to be the center of the fight, either by dropping Wukong's Command or finding a target to build Jingu Mastery stacks on. When both are on the same team, they compete for that initiation role and farm space. The lineup becomes very heavy on melee-range engagement, making it predictable and easy to counter with heroes who can kite or create distance.

This problem gets worse as the game goes on. Enemy teams can itemize with things like Force Staffs and Ghost Scepters to neutralize two threats at once, since both Primal Beast and Monkey King need to be on top of their targets to be effective. Fights become awkward; one hero will often commit their big spells only for the other to be out of position or unable to contribute effectively. The team composition often ends up lacking the ranged damage or control from other angles needed to finish off enemies after the initial chaos, leaving both heroes feeling a little redundant.