To represent the geographical challenge posed to the Monos by Aer's height.
I love this kind of effect. Also, I've been trying to think up mechanical themes for the Aerians (maybe we should go with Aerites or something...), and card drawing and loving it are my recent thought.

Good flavor, strange mechanic. Why would I attack you if my creature was going to be blocked and you would draw a card? Without other shenanigains ("Target creature must attack" for example) this card just operates like a poor Ghostly Prison.

This card would seem like a fine card if the "that creature becomes blocked" phrase was removed (and this card's casting cost adjusted accordingly)... but then it doesn't get the flavor across. Hmm...

Maybe this would make a better instant? ­

You're quite right. As is, a similar effect would work better as an instant. Here's two different enchantment possibilities:
"Creatures can't attack you unless their controller pays for each creature that's attacking you.
Whenever a creature attacks you, you may draw a card."
Or:
"Creatures can't attack you unless their controller pays for each creature that's attacking you.
At the end of each opponent's turn, you may draw a card for each creature that player controls that didn't attack this turn."
I like the flavor of the second one better, though it's a bit bizarre in that it encourages your opponent to attack you.

Ah, yes, those are better. I have no preference... they both have their charms.

The instant could still work, also. We'll keep it open ended and see if a hole needs filling.

I like basic idea of this being a Ghostly Prison that triggers Enlighten, but I don't like the current effect. It's never going to trigger the card draw. My other suggestions are okay (I made them so long ago it feels like another person did), but I don't know that either should be uncommon. New votes for cost and effect:

• : "Creatures without flying can't attack you or a planeswalker you control unless their controller pays for each creature that's attacking you."
• : "Whenever a creature without flying attacks you or a planeswalker you control, draw a card unless that creature's controller pays ."

Hm. So the first is a Ghostly Prison, the second is a riff on Rhystic Study. Yep, both are better than the current effect. I think I prefer the second.

Agree.