Dethrone puts a +1/+1 counter on a creature whenever it attacks the player with the most life or tied for most life. Introduced in Conspiracy, the mechanic was designed for multiplayer, nudging the table to keep attacking whoever is currently ahead.
Marchesa, the Black Rose gives every other creature you control dethrone and returns dying creatures that have +1/+1 counters, while Scourge of the Throne grants an extra combat when it swings at the life leader. Since life totals start high in Commander, dethrone creatures tend to grow early and often.
