The Wildcat should be worded:
Whenever ~this~ deals combat damage to a player, you may turn target non-token creature that player controls face down. It's a 2/2 creature.
Done
I have power-level concerns with most of the other cards. Two-power evasive creatures for two mana with saboteur abilities are much too strong. The Dryad is essentially three power for two mana with evasion.
By comparison, Jotun Grunt is essentially a 4/4 for two, and it doesn't require two different off color mana. At least with the Grunt you can fuel him yourself, so the Dryad is much more metagame dependent. So, I think it's fair.
The Knight is fine power-wise, but both his abilities feel red.
Hmmm. You have a point. Should the ability RFG or shuffle into library instead of destroy?
The Sprite is just too strong. Returning lands to someone's hand is never a minor ability.
*Nonbasic lands. There's a big difference. On turn three, you could play Back to Basics, Blood Moon or Crucible of Worlds, and are those cards overpowered? The flavor/ability is modeled after Plow Under. I could add "unless that player pays 2" to the end of the ability if it is, indeed, too powerful.
The Curate is too strong as well as shadow might as well say unblockable. I think the evasion abilities are too strong on these types of cards.
Remember you're putting into play the opponent's creatures, not your own. This was important to avoid Squee like discard situations or infinately recuring Children of Korlis. Really, this guy is only good against Zoo and possibly Survival. Do you think he's better than Goblin Lackey? I certainly don't. EDIT: I've completed the Reanimate ability by including life loss.
Remember that they still die to the most basic forms of removal: StP, Lightning Bolt, Pyroclasm, Darkblast. Plus, the double mana requirement makes them very specific, and can't easily be splashed for.
Cards from the same cycle should have the same rarity.
Okay. For some reason I thought the multicolor creature cycle in Invasion didn't.
EDIT: I've done a LOT of balancing. You decide if I've nerfed them too much.