Which hero’s permanent buff is the scariest?

I generally feel like permanent stacks of most heroes is usually not super relevant (0 stacks means your game is hard already, many stacks means you’re probably already winning in gold/xp). Which heroes are the most dependant/powerful with their permanent stacks in your opinion?

Imo it’s necro, games where I get to use scythe on cool-down feel completely free after a certain point.