I know this effect is easily broken, which is sad.
I was originally going to put this on a white weenie commander, but having this on a low-cost white creature would never work. Then I considered making it a four-color creature, and then a four-color enchantment, but I couldn't decide what color should be missing. It seems to me it should be red or green, but I can't decide which one.

I agree that's very interesting. Play all your creatures as 1/1s for a discount.

How about making creatures spells cost less where X is their average P/T (or some similar wording that could be templated)? (Or possibly of any colour less, although I think that would be complicated.) Then you can at least play creatures as 1/1 for a semi-reasonable discount, and it may be too good for some creatures with powerful abilities, but at least it doesn't let you play Emrakul, the Aeons Torn as a 1/1 for ?

No, that would make Emrakul cost , if I read your comment right. lol
Maybe I could make it only do colored creatures... Although man, this would be infuriating with Iona, Shield of Emeria, or Elesh Norn, Grand Cenobite, or any of the Praetors, really. sigh

Oops, good point. Yeah, I don't know.

Definitely an interesting concept, but it's also very hard to find an appropriate drawback.

If it weren't for weird layering issues, I'd suggest having it just remove abilities from creatures, but then you need a static P/T value. Which would make the design fairly pointless.

The best drawback for this is probably making it cost a lot itself.

­:(

Well, technically, it comes with it's own drawback built-in: The fact that the creatures you really want to play with this card will not share the same mana base as this card. For example, this card is an awesome way to cheat a Divinity of Pride, and the rest of the avatar cylce in Morningtide, into play for ... but you normally wouldn't put that card in a deck that played 4 colors.

It's true, though, that this card breaks when paired up with cards like Triskellion. Find a way to return that card to your hand (Skeleton Shard perhaps?), and you have one hell of a machine gun. Since the card now costs 6, that's probably fair. I really wish, however, that you could find a reasonable way to make this card not allow you to play creatures with a casting cost greater than 7, though. Well, a way that wasn't all icky.

Well, I restricted it to colored creatures, so at least now it doesn't break artifacts.