Target creature and all other creatures with the same name as that creature get +2/+2 until end of turn.
3/16/2018 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.
3/16/2018 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.
3/16/2018 The name of a creature token is the same as the creature types it was created with, unless the token is a copy of another creature or the effect that created the token specifically gave it a different name. For example, a 1/1 Cat Soldier creature token is named “Cat Soldier.”
3/16/2018 A face-down creature has no name, so it can’t share a name with anything. This includes other creatures with no name.