According to the Legend rule, Legendary Creatures - or simply Legends - can be summoned only if a Legend with the same name as the one a player would like to summon is not already in play.
This obviously means that two identical legendary creature cards cannot be simultaneously present on the battlefield; but it also means that no player can summon cards like Clone, or Copy Artifact, if their owner chooses a Legend as the artifact creature or creature to copy.
For example, if Traxos, Scourge of Kroog is in play, any player cannot cast Copy Artifact and choose to copy Traxos.
Or if it does, Copy Artifact immediately ends up in its owner's graveyard.
Assuming that what is reported is correct, the question is then the following:
- A player has on the battlefield Vesuvan Doppelganger, who has already copied another creature in play.
- Later in the game, the opponent summons Slimefoot, the Stowaway.
- In the next upkeep phase, the player controlling Vesuvan Doppelganger then intends to copy it.
- However, if the latter chose Slimefoot as the object of his next transformation, the Vesuvan Shapeshifter would be immediately taken to its owner's graveyard.
Is everything reported correct?