Shadow Fiend + Venomancer

Why this works

Drafting these two heroes together often forces a difficult choice about how your team is going to secure kills. Shadow Fiend relies on getting the last hit for Necromastery souls, but all of Venomancer's spells apply damage-over-time that can easily secure the kill by accident. This actively denies Shadow Fiend his core mechanic. Furthermore, Venomancer provides slows but lacks the hard stuns that Shadow Fiend needs to reliably land multiple Shadowrazes or set up a devastating Requiem of Souls. A slow simply isn't enough to hold a target in place.

This tension between burst and attrition defines the game. Fights get messy as Venomancer wants to spread his poison and kite, while Shadow Fiend wants to stand his ground and unload on a single target. Without proper setup, SF has a much harder time finding an opening to delete a key hero. The team gets pulled in two different directions, with one hero wanting long, drawn-out engagements and the other needing quick, decisive ones. This lack of a single, coherent plan gives opponents an advantage in any teamfight.