Yay! Flying horseys! Before I start on each card, I want to remind people that even though these all require a Spirit or Arcane spell, there are a lot more Spirits than you probably think there are (white has 89, blue has 66, black has 86, red has 41, green has 64, and there are 2 colourless ones; not including cards with Changeling), so that won't count against them.
Easily the worst flying horsey. Its effect isn't that bad but the cost is way off. This should not cost 7, plain and simple. Even if it's a moderately beefy green flier.
Pros: Moderately beefy green flier
Cons: Weak effect, too expensive
As long as you limit yourself to not casting Spirit or Arcane spells with a CMC of 4, you're golden with this card. I've made an EDH around it and it's pretty fun. If only there was a 0-cost Spirit or Arcane spell I could put in there...
Pros: Wraths with regularity
Cons: Makes you want to avoid the number 4
Mill can be fun, and this card is really effective at it. The only real thing I have against this is that milling itself isn't that strong usually, so you be having fun with this, but you might not be winning.
Pros: Super easy mill
Cons: Mill is weak
Another card that makes me want a 0-cost Spirit or Arcane spell. It's very much like Celestial Kirin in that it's pretty awesome and you have the added bonus of not needing to avoid the number 4!
Pros: Super effective control
Cons: Dies to Murder
I really, really, wish they had added "that creature gains haste" to this card's effect line. It can still be fun with different sack effects or standing haste-giving effects (like Burst of Speed), but otherwise this card was really hobbled by that omission.
Pros: Temporary creature steal
Cons: Doesn't give stolen creatures haste