Naga Siren + Skywrath Mage

Why this works

Setting up a big teamfight with Song of the Siren can look promising, but it has a core problem for Skywrath Mage. Sleeping enemies are invulnerable, which means casting Mystic Flare on them wastes its initial, most important damage. By the time Naga Siren ends the song, the enemies are often awake and have enough time to walk out of the damaging area before it can really hurt them. The timing has to be perfect to get any value, and a small mistake from either player means the entire setup does nothing.

Outside of that difficult combo, their goals don't really overlap. A Naga Siren is usually focused on farming with illusions and applying pressure across the map, while Skywrath Mage wants to be active early, looking for kills with another teammate. While Ensnare can hold a single target down for Skywrath's spells, it's a basic setup that many other heroes can provide more reliably. For the most part, they end up playing separate games on the same team, neither helping nor hindering the other's plan in a significant way.