If the mana cost of the revealed card includes , X is considered to be 0.
If the revealed card doesn’t have a mana cost (because it’s a land card, for example), its converted mana cost is 0.
The converted mana cost of a split card, such as cards with aftermath from the Amonkhet block, is based on the combined mana cost of its two halves.
Raid abilities care only that you attacked with a creature. It doesn’t matter how many creatures you attacked with, or which opponent or planeswalker controlled by an opponent those creatures attacked.
Raid abilities evaluate the entire turn to see if you attacked with a creature. That creature doesn’t have to still be on the battlefield. Similarly, the player or planeswalker it attacked doesn’t have to still be in the game or on the battlefield, respectively.
Some raid abilities trigger at the beginning of your end step. These abilities trigger if you attacked with a creature that turn, even if the card with that raid ability wasn’t on the battlefield when you attacked.