Aye, I tried balancing this using blessing, Lycanthrope, and Liquid Shadow. I kinda felt like the one turn delay would be necessary because one could play this on a creature that's already been out a turn or so and use the ability (Sauce: Mitosis on creatures already out for a turn), then play again, use ability, play again, use ability. The one turn delay forces one to space out the ability.
Maybe that makes it seem UP, but gaining +5|+5 per card is pretty powerful. Throwing in that CP is in element already and darkness has vamps...Honestly I think this could lead to OP combos, I honestly considered making this card more expensive and still kinda feel like I should.