Flying, vigilance, haste

Play with the top card of your library revealed.
You may cast instant and sorcery spells from the top of your library.
Whenever you cast an instant or sorcery spell from your library, copy it. You may choose new targets for the copy.

Target creature gets +1/+1 until end of turn for each creature you control.

Counter target spell unless its controller pays .

Flash (You may cast this spell any time you could cast an instant.)
When Mizzium Meddler enters the battlefield, you may change a target of target spell or ability to Mizzium Meddler.

Enchant creature
At the beginning of each upkeep, if enchanted creature is untapped, tap it.

Constellation — Whenever Oakheart Dryads or another enchantment enters the battlefield under your control, target creature gets +1/+1 until end of turn.

Flying
Megamorph (You may cast this card face down as a 2/2 creature for . Turn it face up any time for its megamorph cost and put a +1/+1 counter on it.)

You have hexproof. (You can't be the target of spells or abilities your opponents control.)
If a creature would deal damage to you, prevent 1 of that damage.

Whenever Ornery Goblin blocks or becomes blocked by a creature, Ornery Goblin deals 1 damage to that creature.

Enchant creature
Enchanted creature gets -6/-0.

When Pitchburn Devils dies, it deals 3 damage to any target.

First strike
Landfall — Whenever a land enters the battlefield under your control, Plated Geopede gets +2/+2 until end of turn.

: Monstrosity X. (If this creature isn't monstrous, put X +1/+1 counters on it and it becomes monstrous.)
When Polukranos, World Eater becomes monstrous, it deals X damage divided as you choose among any number of target creatures your opponents control. Each of those creatures deals damage equal to its power to Polukranos.

Attacking creatures get +2/+0 until end of turn.
Cycling (, Discard this card: Draw a card.)

Put target creature card from a graveyard onto the battlefield under your control. You lose life equal to its converted mana cost.

Haste (This creature can attack and as soon as it comes under your control.)
Reckless Brute attacks each combat if able.

Return target artifact card from your graveyard to the battlefield.

Relentless Rats gets +1/+1 for each other creature on the battlefield named Relentless Rats.
A deck can have any number of cards named Relentless Rats.