Mega creeps:

Mega creeps are the superpowered lane creeps a team gets after destroying all of the enemy's barracks in a lane, making that lane spawn much stronger allied creeps for the winning side.

In Dota 2, mega creeps are a major comeback tool for the team that has lost almost every structure, because the stronger wave pressure can stall an opponent's push and create space to defend high ground. They also matter because they can slowly overwhelm a base if the losing team cannot clear waves efficiently. For example, if Radiant loses all three sets of barracks, every lane begins spawning mega creeps for Dire, forcing Radiant to spend resources defending constant pressure instead of leaving the base to take fights.

Related: Barracks, Creep, High ground