Not for not, but Parapet is normally costed as , even as a common. This is a Parapet with a drawback (if you kill the enchanted creature, you kill the enchantment, too.)

It's a weird problem. I can get why you didn't go +0/+2, because the card stops being a common at that rate (maybe?). I'm not sure how you solve that, and keep the Ambient relevant. I mean, if the Ambient cost , then why would anyone bother paying the for the non-ambient version?

On a separate side note, do you have anyway of dealing with the memory issues this card creates? I know what I'd do: Ambient would lay ontop of creatures, while non-Ambient would lay underneath. It's not exactly something you can enforce, though...

you can do the opposite keyword that turns it into an Aura. so it's only an aura only if you paid the <keyword> cost.