Bane + Shadow Fiend

Why this works

Setting up a kill with this duo looks simple on paper, but often proves inefficient in practice. The core idea is for Bane to use Fiend's Grip to hold a target down for a full-power Requiem of Souls from Shadow Fiend. The problem is timing and positioning. For his ultimate to do maximum damage, Shadow Fiend has to be right on top of the gripped target, which can put him in a very dangerous spot. It also commits two huge ultimates to kill a single hero, which can be a poor trade if the enemy team is nearby and ready to counter-attack once the spells are used.

Beyond that one specific interaction, they don't offer each other much. In lane, they are usually in separate roles and can't support each other's timings. Later on, Bane's other spells can be actively unhelpful. A defensive Nightmare on an ally or an enemy can easily be broken by an errant Shadowraze, ruining the setup. Bane excels at isolating one hero for his team to focus from a safe distance, while Shadow Fiend wants to hit multiple targets at once. They can operate on the same team, but their kits tend to pull the game plan in different directions.