Descend is a family of graveyard mechanics that cares about permanent cards going to or accumulating in your graveyard. Some cards check whether you descended during a turn, while descend 4 and descend 8 require at least that many permanent cards in your graveyard.
Akawalli, the Seething Tower grows as you reach the descend 4 and descend 8 thresholds, and the 8/8 The Ancient One can’t attack or block until you hit descend 8. Self-mill and self-discard effects can quickly stock the graveyard with creatures and lands to switch these abilities on.
