Lifestealer + Timbersaw

Why this works

Trying to secure a mid-game kill exposes the core problem with this pair. Both Lifestealer and Timbersaw want to be in the middle of the fight dealing damage, but neither provides the lockdown needed to make that happen reliably. They lack a single hard stun between them. Lifestealer needs a target held in place to connect and deal his damage, while Timbersaw chips away at enemies with his spells. Against any team with decent mobility or disengage tools, both heroes can be kited and ignored. They overlap in wanting to tear down the enemy frontline, often leaving slippery backline heroes free to control the fight from a safe distance.

This weakness forces their entire game plan to be one-dimensional. Timbersaw pressures lanes early, but Lifestealer can't always convert that pressure into objectives without help. In larger teamfights, the enemy can simply walk away when Lifestealer uses Rage, then turn and burst him down after it expires. Without a setup, the Infest bomb becomes a telegraphed burst of damage that's easy to dodge. The success of this duo relies almost entirely on their supports providing all the catch, putting immense pressure on the draft and leaving very little room for error.