msem-instigator

Flash
Rhapsody {5}{U}{U} (Pay {5}{U}{U} to cast this as a 4/4, or once it is in play to make it become a 4/4.)
Animus Channeler's rhapsody cost can be paid any time you could cast an instant.

You may play an additional land on each of your turns.
Whenever Antali Archdruid attacks, if two or more lands you control entered this turn, Antali Archdruid deals 3 damage to any target and you gain 3 life.

Flash
Flying
Once during each of your opponent's turns, when you cast a spell, you may pay {1}{U/R}. If you do, copy it. You may choose new targets for the copy. (If it's a permanent spell, the copy becomes a token.)

Flying, vigilance
Augmented — When Antigravity Agent enters, if you've spent {W}{U}{R}{B}{G} to cast spells this turn, distribute a flying counter and a vigilance counter among one or two creatures you control.

Colossal 4—{8} (You may cast this for its colossal cost to have it enter with four +1/+1 counters; or pay {8} as a sorcery: Put four +1/+1 counters on it if it has none.)
Abilities you activate that aren't mana abilities cost {2} less to activate. This effect can't reduce the mana in that cost to less than one mana.

Flash
Flying

Apostle of the Elders has lifelink as long as it has a +1/+1 counter on it.

Whenever you foretell a card or cast a foretold spell, each opponent loses 1 life and you gain 1 life.

Distorted (This creature can be blocked by tapped creatures but not untapped creatures.)
When Arbiter of Shal'Iv enters, adjudicate. (Create a white enchantment Aura token with enchant creature and “Sacrifice this token: Untap enchanted creature” attached to target creature.)

When Arcanomancer enters, return up to one target instant card and up to one target sorcery card from your graveyard to your hand.

When Archivist Heretic enters, you lose 1 life, then investigate. (Create a colorless Clue artifact token with “{2}, Sacrifice this artifact: Draw a card.”)

When Arcor-Staff Adherent enters, you may remove all -1/-1 counters from target creature.

Haste
Whenever Arisen Hunter attacks, target player loses 2 life and you gain 2 life.
If Arisen Hunter would die, exile it instead.

Whenever you cast a noncreature spell, each opponent loses 1 life.
{4}, Exile Arisen Psion from your graveyard: Draw a card.

Whenever Arisen Rider attacks, creatures your opponents control get -1/-1 until end of turn.
If Arisen Rider or another creature or planeswalker would die, exile it instead.

Menace, haste
As long as Arleigh, Spellblade Prodigy is tapped, the first spell you cast during each other player's turn costs {U/R} less to cast. This effect reduces only the amount of colored mana you pay. (For example, if you cast a spell with mana cost {1}{R}, it costs {1} to cast.)

Whenever an artifact or enchantment you control enters, Armament Scavenger gets +1/+0 and gains trample until end of turn.

When Armored Valiant enters, creatures you control get +1/+1 until end of turn.

Whenever two or more creatures an opponent controls attack, adjudicate. (Create a white Aura enchantment token with enchant creature and “Sacrifice this token: Untap enchanted creature” attached to target creature.)
Enchanted creatures you control get +0/+2.

When Arms Merchant enters, look at the top four cards of your library. You may reveal an artifact card from among them and put it into your hand. Put the rest on the bottom of your library in any order.

Prowess
When Arms Tinkerer enters, choose one —
• Destroy target artifact.
• Create a Treasure token. (It's an artifact with “{T}, Sacrifice this artifact: Add one mana of any color.”)

Whenever one or more creatures you control deals combat damage to a player, you may sacrifice one of them. When you do, destroy target creature defending player controls, then you and the destroyed creature's controller draw a card.

Haste
Whenever Arpechian Tiger attacks, you may sacrifice a land. If you do, Arpechian Tiger deals 3 damage to target creature or planeswalker.

Trample
When Arpechian Yatte enters, put a +1/+1 counter on each other creature you control.
Whenever another creature you control enters, put a +1/+1 counter on Arpechian Yatte.

{1}{G/W}: Put a +1/+1 counter on Artful Chari.
Whenever you cast an instant or sorcery spell, you may remove a number of +1/+1 counters from Chari equal to that spell's mana value. If you do, copy that spell, and you may choose new targets for the copy.