Invoker + Muerta

Why this works

Stacking up heavy magic damage from two core positions can seem powerful, but it often backfires. An Exort Invoker relies on his big spell combinations to delete targets, while Muerta's ultimate, Pierce the Veil, converts all her attack damage into magical. When both heroes are online and dealing damage, they present a singular threat type. This makes it straightforward for the enemy team to itemize against your strategy. A single Pipe of Insight or a few well-timed Glimmer Capes can blunt the impact of both your primary damage dealers at the same time, forcing your team to fight uphill.

The result is that your teamfights tend to be very all-in. If Invoker's initial combo and Muerta's opening shots during her ultimate don't secure key kills, the duo's damage output can fall off hard. Muerta then finds herself trying to finish off targets with magic damage when they've already built resistance to it, and Invoker has to wait for long cooldowns to contribute again. Other hero pairings force opponents to choose between armor or magic resistance, but this one lets them counter both cores with one set of items.