If the mana cost of a creature card in your graveyard includes {X}, X is 0 for the purpose of determining its mana value.

If another effect causes Alesha's power to be less than the mana value of the target card as its last ability tries to resolve, it won't resolve and none of its effects will happen.

Raid abilities care only that you attacked with a creature. It doesn't matter how many creatures you attacked with or which player, planeswalker, or battle 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, planeswalker, or battle it attacked doesn't have to still be in the game or on the battlefield.

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 permanent with that raid ability wasn't on the battlefield when you attacked.