Sanctum of the Sun

2018-01-19 For more information on double-faced cards, see the Ixalan mechanics article (http://magic.wizards.com/en/articles/archive/feature/ixalan-mechanics).
2018-01-19 If a card in exile has {X} in its mana cost, X is considered to be 0.
2018-01-19 If an object has no mana cost, its mana value is 0. A mana value of 0 can still help unlock Azor's Gateway.
2018-01-19 The ability of Sanctum of the Sun is a mana ability. It doesn't use the stack and can't be responded to.
2018-01-19 The cards you exile from your hand are exiled face up.
2018-01-19 The mana value of a split card, such as a card with aftermath from the Amonkhet block, is based on the combined mana cost of its two halves. A split card doesn't have two mana values.

mtg.wtf