Can't I?

I don't see why not. :)

Too many Spikes!
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Enchantment - Aura
Enchant Creature
Enchanted creature is black.
When ~ enters the battlefield, exile up to two target cards in any number of players graveyards.
­, Discard ~: Search through your library for two auras with a converted mana cost of 1 or less. Your opponent chooses one. Put the chosen card in your hand and the other in your graveyard. Shuffle your library.

I think that, if I ever wrote a children's book, I might name it "Too many Spikes!"

Too many Johnnies!
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Enchantment
Whenever you discard a card, sacrifice a permanent.
Return ~ to your hand: Untap all creatures your opponent controls. Creatures you control must block, if able.

Too many Timmies!
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Sorcery
Name a creature type, then roll a six sided die. Each creature that has the named creature type gains a +X/+X counter where X is equal to the die number rolled.
Any player may copy this spell by paying .

That may be the best cycle I've ever designed. ;)

The Johnny one made me LOL :)

I don't think Alex meant you couldn't design a +7/+7 aura at common literally, but rather than you couldn't make something that functioned similarly to vanilla +7/+7 pump, however, now you've got me curious, could you design a +7/+7 aura?

"Too many spikes" is a good effort, but I still don't think would be printable at common -- it's not immediately broken, but I think a card that can either make a 10/10 blocker (or make your opponent's bomb not attack) is probably too intrusive for common. And I think "enchanted creature gets +7/+7 and can't attack or block" is too niche for common. Maybe "design a +7/+7 common aura" should be the next design challenge? :)

ETA: Maybe if the creature slowly died, like unstable mutation? Not that that's very common.