Grimstroke + Viper

Why this works

Landing Soulbind on two targets lets Viper follow up with a duplicated Viper Strike, locking down both enemies with a crippling slow and heavy damage over time. This makes it almost impossible for linked heroes to escape a gank or teamfight. Even without the ultimate, Grimstroke’s other slows from Stroke of Fate or the stun from a charged Ink Swell can give Viper the setup he needs to get in position and start applying his corrosive damage. This combination provides a way to reliably catch and burst down two heroes at once, which is always a useful tool to have.

The problem is that this entire dynamic relies on two long-cooldown ultimates being available at the same time. When either Soulbind or Viper Strike is down, the potent synergy vanishes. Outside of that specific combo, the heroes don't offer each other much. Viper wants to be a durable front-liner, consistently applying pressure, while Grimstroke plays from the back with his spells. Good opponents can exploit this by forcing fights when the ultimates are on cooldown, leaving the pair with a much less coordinated game plan.