Cerebral Eruption

• WWizards of the Coast2011-01-01
  Official Ruling
  The mana value of the revealed card is determined solely by the mana symbols printed in its upper right corner. The mana value is the total amount of mana in that cost, regardless of color. For example, a card with mana cost has mana value 5.
• WWizards of the Coast2011-01-01
  Official Ruling
  If the targeted opponent is an illegal target by the time Cerebral Eruption resolves, the spell doesn’t resolve. No cards will be revealed and no damage will be dealt.
• WWizards of the Coast2011-01-01
  Official Ruling
  If a land card is revealed this way, Cerebral Eruption is returned to its owner’s hand from the stack. It finishes resolving, but it isn’t put into the graveyard.
• WWizards of the Coast2011-01-01
  Official Ruling
  Once the card is revealed, it’s too late for players to respond. The targeted opponent can’t, for example, see how much damage will be dealt, then cast a damage prevention spell or activate a regeneration ability. All such actions must be done before Cerebral Eruption starts to resolve.
• WWizards of the Coast2011-01-01
  Official Ruling
  If the mana cost of the revealed card includes , X is considered to be 0.
• WWizards of the Coast2011-01-01
  Official Ruling
  If the revealed card has no mana symbols in its upper right corner (because it’s a land card, for example), its mana value is 0.

Rulings via Scryfall