Viper + Winter Wyvern

Why this works

Setting up a kill with Winter's Curse often works against what Viper wants to do. The main target of the curse is immune to all damage from your team, which means Viper's Viper Strike and Poison Attack do nothing to them for the duration. Winter Wyvern's ultimate is a setup for a massive burst of damage, but Viper provides sustained, grinding damage-over-time. While he can still place Nethertoxin under the clump of enemies attacking their ally, his primary single-target pressure is completely shut down by his own teammate's spell. This fundamental clash of styles makes their ultimates actively work against each other.

Early on, the lane can feel strong. The combined slows from Viper and Winter Wyvern can make it nearly impossible for an enemy to escape. The issues appear later in teamfights where a single miscommunication can be costly. If Viper commits his ultimate to a target that Wyvern then curses, Viper is forced to wait or switch targets, splitting the team's focus. To make this duo work, Viper has to hold his spells until after the curse ends, which can be too late. The heroes want to initiate and control fights in fundamentally different ways, leading to inefficient and awkward engagements.