Venomancer + Void Spirit

Why this works

Chasing down enemies after a Poison Nova can feel awkward for this pair. Void Spirit wants to unload his entire spell combination on a single hero to burst them from full health. Venomancer, on the other hand, deals his damage over a long duration, slowly draining the enemy team and setting them up to be finished off by right-clicks or small spells. This means Void Spirit either uses his full combo on a target that was going to die to poison anyway, or he lacks the tools to effectively clean up multiple low-health opponents who scatter after Venomancer's ultimate.

As a result, their teamfight contributions can feel disconnected. Venomancer makes the entire enemy team slow and vulnerable, but Void Spirit is really looking for a single target to be locked down by a hard stun, which Veno doesn't provide. While the slows from Venomous Gale certainly help Void Spirit land his spells, the overall game plans of the two heroes don't align perfectly. They can function on the same team, but they rarely create openings for each other in the way more specialized duos might.