Shadow Fiend + Viper

Why this works

Putting these two cores on the same team creates a fundamental conflict over farm and tempo. Both Shadow Fiend and Viper want to be the centerpiece of the mid-game, hitting item timings and then forcing fights to press their advantage. They occupy similar farming patterns and want to play in the same areas of the map, leading to inefficient use of resources. The heroes also offer overlapping strengths, focusing on heavy damage output rather than complementing each other's weaknesses. A team with both can feel short on the hard lockdown or utility needed to enable a primary damage dealer.

As the laning stage ends, this tension becomes clear. The game plan relies on overwhelming the enemy with damage, but without reliable stuns, that damage is hard to secure. An enemy team can often split their focus or disengage from fights too easily. While Viper can slow a target with Viper Strike, it isn't enough to hold an entire team in place for a big Requiem of Souls from Shadow Fiend. This leaves the lineup feeling one-dimensional and vulnerable to being controlled, as neither hero provides the setup needed to let the other truly dominate a teamfight.