Consider the fact that every game has its own die-hard fans who hang on to every character and lore tidbit, and things get even tougher
The first is that he has to deal combat damage, which means he likely has to use his own ability to grant himself unblockable, costing a bit of mana
The protection the sword gives means that not only can your opponent not target the creature with spells and abilities, much like Hexproof, but also means that their creatures, planeswalkers, and other permanents cannot interact with it either
Avoid mass-produced variants, high-pop cards without character significance, and pure speculation plays
Check the print quality and cardstock (real cards have a distinctive blue inner core visible from the edge), the rosette pattern on the back, the security stamp on planeswalker / mythic cards from recent sets, and confirm the collector number and set code match the official Scryfall record
That said, three cards have returned from being Forbidden to now being newly Limited, and the first one was one everyone saw coming a mile away, being Metamorphosis