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Target creature and all other creatures with the same name as that creature get +2/+2 until end of turn.
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."
A face-down creature has no name, so it can't share a name with anything. This includes other creatures with no name.
Echoing Courage has only one target. Other creatures with that name are not targeted. For example, a creature with protection from green will still get +2/+2 if it has the same name as the target creature.
If the target creature is an illegal target by the time Echoing Courage tries to resolve, the spell doesn't resolve. No creatures get +2/+2.
