Viper + Weaver

Why this works

Trying to kill a single hero is where the friction shows. Viper can apply Viper Strike, massively slowing the target and setting up a chase. Weaver can then easily stay on top of them with Shukuchi. The problem is that neither hero has a stun. A simple teleport scroll, Force Staff, or a well-timed defensive spell from a support is often enough for the target to survive the initial gank attempt. Their damage types also don't amplify each other; Viper's magic damage gets no benefit from Weaver's armor reduction, and they end up feeling like two solo heroes fighting near each other.

This lack of control becomes a major liability as the game progresses. The Viper wants to force fights and take objectives in the mid-game, but the lineup lacks the tools to initiate properly. The enemy team can often split them up, bursting down the fragile Weaver before he can have an impact or simply walking past the slow Viper to kill his backline. Without a solid frontliner or a strong teamfight stunner to pair with them, they leave too many openings for an opponent to exploit their disconnected timings and kits.