Mesmerizing Siren

Flying & Bestow {4}{p/u} (If you cast the card for its bestow cost, it's an Aura spell with enchant creature. It becomes a creature again if it's not attached to a creature)
You control the enchanted creature & it gets
+1/+1 & Flying, if you own the creature it
gains {2} Ward. If you do not own it, then it's owner may pay {4} to disenchant it.