Nature's Prophet + Riki

Why this works

Setting up a gank with Sprout can be awkward for an allied Riki. While the ability traps an enemy, the trees also block Riki from freely attacking, forcing him to use Blink Strike to get inside and leaving him with limited room to maneuver. Smoke Screen is already a powerful zone for Riki to fight in, and Sprout doesn't add a guaranteed stun or disable to make it significantly better. Both heroes excel at creating pressure by themselves across the map, but their kits don't directly amplify each other in fights.

Across a game, this pairing often results in two heroes playing separate games. Nature's Prophet will apply pressure to lanes with his Treants while Riki looks for solo pickoffs elsewhere. When forced into a full teamfight, the lack of a durable core or reliable lockdown from this duo becomes a problem. The enemy team can often group up with detection to nullify Riki's threat and burst down the fragile Nature's Prophet. This forces the rest of your lineup to provide all the hard initiation and survivability that these two heroes lack.