Select an enemy follower on the field. Deal it 3 damage and give +1 to each follower that costs 1 or less on your field.
QIf there are no selectable enemy followers on the field, can I still play this spell to give my followers that cost 1 or less +1 attack?
ANo, you can't. If a spell requires you to select a target, and there are no valid targets on the field, that spell cannot be played at all.