Flying, soulbond (You may pair this creature with another unpaired creature when either enters. They remain paired for as long as you control both of them.)
As long as Breathkeeper Seraph is paired with another creature, each of those creatures has "When this creature dies, you may return it to the battlefield under its owner's control at the beginning of your next upkeep."

Whenever a permanent an opponent controls is put into a graveyard, put that card onto the battlefield under your control unless that opponent pays 3 life.

Changeling (This card is every creature type.)
Flying

Exile target creature. Its controller gains life equal to its power.

You gain life equal to the damage dealt to you this turn. Simulacrum deals damage to target creature you control equal to the damage dealt to you this turn.

Enchant creature
Cumulative upkeep (At the beginning of your upkeep, put an age counter on this permanent, then sacrifice it unless you pay its upkeep cost for each age counter on it. can be paid with one mana from a snow source.)
Enchanted creature gets +3/+3 for each age counter on this Aura.

Flying, trample
Whenever an opponent searches their library, that player sacrifices a creature of their choice and loses 10 life.
Whenever another creature dies, put a +1/+1 counter on Ob Nixilis.

Haste
Armour of Shrieking Souls — When Lucius the Eternal dies, exile it and choose target creature an opponent controls. When that creature leaves the battlefield, return this card from exile to the battlefield under its owner's control.

Prototype — 3/3 (You may cast this spell with different mana cost, color, and size. It keeps its abilities and types.)
Flying
At the beginning of combat on your turn, target creature you control gains your choice of flying, vigilance, or lifelink until end of turn.

Vigilance
: Create an 8/8 Beast creature token that's red, green, and white.

Flash
Vigilance
When this creature enters, any number of other target creatures you control phase out. (Treat them and anything attached to them as though they don't exist until their controller's next turn.)

You can't cast Serra Avenger during your first, second, or third turns of the game.
Flying, vigilance

Power-up — : Put two +1/+1 counters on Nick Fury, then look at the top seven cards of your library. You may put a Hero, Equipment, or Vehicle card from among them onto the battlefield. If it's a double-faced card, you may transform it. Put the rest on the bottom of your library in a random order. (Activate each power-up ability only once. Reduce the cost by his mana cost if he entered this turn.)

Flash
When Yuriko enters, choose one —
• Target creature gets -X/-0 until end of turn, where X is the number of cards in your graveyard.
• Surveil 2. (Look at the top two cards of your library, then put any number of them into your graveyard and the rest on top of your library in any order.)

Destroy target creature with total power and toughness 5 or less.

: This creature deals 1 damage to each creature without flying.

Other Pirates you control get +1/+1.
At the beginning of your end step, gain control of target nonland permanent controlled by a player who was dealt combat damage by three or more Pirates this turn.

Level up (: Put a level counter on this. Level up only as a sorcery.)
LEVEL 1-2
0/1
: Draw a card, then discard a card.
LEVEL 3+
0/1
: Draw a card.

Flying
At the beginning of your end step, you may sacrifice another creature. When you do, Ziatora deals damage equal to that creature's power to any target and you create three Treasure tokens.

(: Add .)