mtg xx cards How do you determine the value of X in a Magic the Gathering spell's casting cost when there are multiple X's? X

Nahiri is bringing Emrakul into your world

You may use abilities that play as fast effects multiple times before sacrificing the permanent, such as Knight of Dusk's " Your Hand - A Precious Resource Of the three cards you draw at one time, only the top card is revealed, and that card is considered your hand

'Cannot be countered' Spells & Effects: Vexing Shusher and Boseiju, Who Shelter's All are the best way to push through Erayo as she effectively does nothing with these two on the board

They also result in a delayed trigger that does the killing, which you can avoid with stifles or end-the-turn cards like Sundial of the Infinite