Nezumi Freewheeler // Hideous Fleshwheeler 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

Menace When this creature enters, each player mills three cards. (To mill three cards, a player puts the top three cards of their library into their graveyard.) : Transform this creature. Activate only as a sorcery. ( can be paid with either or 2 life.) Menace (This creature can't be blocked except by two or more creatures.) When this creature transforms into Hideous Fleshwheeler, put target permanent card with mana value 2 or less from a graveyard onto the battlefield under your control.