Phoenix + Pudge

Why this works

Setting up a Supernova is much more reliable when Pudge can hold a target in place. A good Meat Hook into Dismember provides the perfect window for Phoenix to position its ultimate. While the channel doesn't last for the full Supernova duration, it forces a key enemy to sit in the damage area and eat the stun. Phoenix can also apply Fire Spirits to the locked-down target and anyone else nearby. The resulting attack speed slow makes it extremely difficult for the enemy team to focus and destroy the egg before it goes off, even if they aren't the one being held.

This combo creates significant kill threat in the mid-game, which can translate into objectives and map control. The enemy team has to adapt by playing more spread out to make landing a multi-hero Supernova harder and to avoid a hook turning into a lost teamfight. Their main counter-play is to try and burst Phoenix from a distance before the egg comes out, or have saves ready for the Dismembered hero. Since the setup relies on Pudge landing a key skillshot and both heroes having their ultimates ready, it isn't a constant threat.