Queen of Pain + Viper

Why this works

Putting these two heroes on the same team often creates a major tempo conflict. Both Queen of Pain and Viper want to be the primary space-creator, using an early power spike to secure kills and farm the aggressive parts of the map. Their kits overlap in ways that don't add much value. You get a lot of slows and magic damage over time, but no hard stuns or lockdown to actually guarantee kills on slippery targets. An enemy stacking early magic resistance also gets double value, effectively countering a huge portion of your team's entire damage output with one or two defensive items.

This problem usually comes to a head in the mid-game. You end up with two cores trying to do the same job, often competing for farm and getting in each other's way. Since neither can truly pin an enemy down, they frequently have to commit together for ganks, which is inefficient. If this duo falls behind, the team has very little late-game scaling or tower-pushing power to fall back on. The opponent's win condition becomes clear: group up with Black King Bars, knowing both Viper and Queen of Pain lose most of their impact once their spells are ignored.