Rise to the Challenge
Creatures you control get +1/+1 for each opponent
Each other player draws a card, you draw a card for each other player.
Not quite sure how this should be costed. In my experience the average multiplayer game is about 4 people.
This would probably also translate well to things like tokens and life gain and ramp.
Destroy target creature unless its controller puts the top half of his or her library into his or her graveyard.
The illusion of choice is the most treacherous leash.
Enchant creature with flying.
You control enchanted creature.
Creature-Viashiano Wizard (uc)
Players can't cast green spells
Familiarity is the greatest weapon of all. The more you are like your enemy, the more of their weaknesses you know.
I fully admit that this effect would probably be more at home in white, but the flavor came to me in a more green way.
Also, it pains me to know that Viashinos being their own creature type absolutely ruins any chance to see "Creature-Lizard Wizard" on a card.
Glimpse of Dreamscape
Sacrifice Glimpse of Dreamscape: For each enchantment put into your graveyard from the battlefield this turn, search your library for a basic land and put it onto the battlefield tapped. Then shuffle your library.
Originally had this at , but I don't think there needs to be a card that much better than Rampant Growth.
The enchantment focus might make this work at , but I'm not sure.
World Half Empty
Target player loses half of his or her life, discards half of his or her cards, sacrifices half of his or her permanents, puts the top half of his or her library into his or her graveyard, and exiles half of his or her graveyard, all rounded up.
I was rather pleased with myself when I came up with this one. Feels really weird to use that many 'his or her's on a card, but alas.