Descend is an ability word — a label that ties together abilities caring about your graveyard. Descend N checks whether you have N or more permanent cards in your graveyard. Permanent cards are creature, artifact, enchantment, land, planeswalker, and battle cards; instants and sorceries don't count. For example, Descend 4 might give a creature +2/+0 or flying as long as you have four permanent cards in your graveyard, while Descend 8 could restrict when you can activate an ability to return a card from your graveyard to the battlefield.
In play, Descend rewards filling your graveyard with permanents, turning a normally lost zone into a resource. Self-mill, sacrifice, discard, and creature combat all help you reach the threshold. Decks built around Descend want to trade creatures, cast permanents, and use effects that put cards into the graveyard, then cash in on the payoff.
