Mars + Phoenix

Why this works

Trapping heroes in Arena of Blood for a Supernova seems powerful, but the two spells often fight for space. Enemies standing outside the wall can usually still attack the egg, while Mars's own teammates might find themselves blocked by the Arena. Mars excels at pinning targets for follow-up physical attacks, an effect that is largely wasted on Phoenix. Phoenix's area-of-effect spells are already good at hitting scattered targets, so the hard containment from Arena doesn't add as much value as it would for a different kind of hero. The lockdown is often redundant.

As the game goes on, both heroes try to anchor teamfights with long-cooldown ultimates that don't directly protect each other. A smart opponent can often focus the Supernova down while ignoring Mars, or simply walk away from the Arena and re-engage after the egg is handled. It creates a split-focus problem where the enemy gets to choose which threat to neutralize first. This pairing requires very precise coordination to overcome the awkward positioning, and often feels less impactful than having the two ultimates available for separate situations.