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."

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

The mana value of a token that isn't a copy of another object is 0. A token that is a copy of another object has the same mana value as that object.

Legion's End targets only one creature. Other creatures will be exiled even if they have hexproof, and cards in its controller's hand and graveyard will be exiled even if that player has hexproof.

If the target creature is an illegal target by the time Legion's End tries to resolve, the spell doesn't resolve. No player reveals their hand, and nothing is exiled.

A face-down creature has no name, so it can't share a name with anything. This includes other creatures with no name.