Summon 2 Forest Bat tokens.
Select an enemy follower on the field and deal it X damage. X equals the number of Forest Bat tokens on your field.
QCan spells such as Night Horde and Fiery Embrace be played when there are no enemy followers on the field that can be selected?
ANo. If the card text explicitly instructs you to "select" a target, and there are no cards that can be selected, then you cannot play the card or pay any associated costs.
QIf my field has reached its card limit, and there is an enemy follower on the field that I can select, can I play this spell?
AYes, you can.