You receive master phase actions during your master phase. A master phase action represents your personal activity during the turn as a Methuselah.
By default, you receive only one master phase action, but some cards may change this amount. You may use a master phase action to play a master card, and some cards can give you alternate ways to use your master phase actions. For example, you can use a master phase action to mark a Red List minion (see section 11). If you've played an out-of-turn master card against this master phase (even if it was cancelled), then you gain one fewer master phase actions than normal (see Master Cards, sec. 1.6.2).
If other effects happen during your master phase, you choose the order in which these effects and your master phase actions are performed.
You cannot save master phase actions for later; master phase actions not used during this phase are lost.