Muerta + Slardar

Why this works

Applying Corrosive Haze to a target is usually a death sentence, but the value is lost on Muerta during her ultimate. Pierce the Veil converts all her attack damage to magical, meaning she gets zero benefit from the armor reduction Slardar provides. The primary damage amplifier from one hero is completely negated by the other's main teamfight spell. This core conflict means they actively work against each other when trying to burst down the same high-priority enemy, which is what you'd expect from this kind of pairing.

This forces an awkward choice in fights. Either Slardar uses his ultimate on a secondary target, or Muerta forgoes her own ultimate to deal physical damage. More often, they simply don't focus the same hero, which splits their impact. Slardar can still set up kills with Slithereen Crush, and Muerta can still execute low-health enemies. However, their peak power moments are fundamentally at odds, preventing them from achieving the clean, focused takedowns that lineups like this are supposed to create, leading to messy and unpredictable fights.