Seasonal Sequels is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

Pitch the titles of up to X holiday-themed sequels to target spell. Copy that spell for each title pitched, except the copy has that name. You may choose new targets for the copies. (Simply adding numbers isn't festive enough.)