Blood Age General

• WWizards of the Coast2021-04-16
  Official Ruling
  Blood Age General’s activated ability affects only Spirits that are attacking as it resolves. If you activate it while no Spirits are attacking, it will have no effect, even if you attack with one or more Spirits later in the turn.
• WWizards of the Coast2021-04-16
  Official Ruling
  Once the activated ability resolves, Spirits that get the +1/+0 bonus will retain it until end of turn, even after they stop attacking or if they stop being Spirits.

Rulings via Scryfall