Evil Twin

Unless a token is a copy of another permanent or was explicitly given a name by the effect that created it, its name is the subtypes it was given when it was created plus the word "Token." For example, if an effect creates a 1/1 Soldier creature token, that token is named "Soldier Token."

Any enters-the-battlefield abilities of the copied creature will trigger when Evil Twin enters the battlefield. Any "as [this creature] enters the battlefield" or "[this creature] enters the battlefield with" abilities of the chosen creature will also work.

If the chosen creature has {X} in its mana cost, X is considered to be 0.

If the chosen creature is a token, Evil Twin copies the original characteristics of that token as stated by the effect that created the token. Evil Twin is not a token in this case.

If the chosen creature is copying something else (for example, if the chosen creature is another Evil Twin), then your Evil Twin enters the battlefield as whatever the chosen creature copied.

If Evil Twin somehow enters the battlefield at the same time as another creature, Evil Twin can't become a copy of that creature. You may choose only a creature that's already on the battlefield.