msem-instigator

Flying
When Arcanum Owl enters the battlefield, you may return target instant or sorcery card from your graveyard to your hand.

When Archaeomancer enters the battlefield, return target instant or sorcery card from your graveyard to your hand.

Flying
Concord — When Archangel of Accord enters the battlefield, if there are four or more card types among permanents you control, destroy all other creatures.

When Architect of the Derezzed enters the battlefield, create two 1/1 colorless Servo artifact creature tokens.
Sacrifice an artifact: Target creature can't be blocked this turn.

When Archive Guardian enters the battlefield, return target card from your graveyard to your hand.
Recite {1}{B}{G} (You may cast this creature from your graveyard for its recite cost. If you do, exile it when it enters the battlefield or if it would leave the battlefield.)

When Archivist Heretic enters the battlefield, 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 the battlefield, you may remove all -1/-1 counters from target creature.

Wanderlust — When Ardent Explorers enters the battlefield, if you control four or more differently named lands, create a 1/1 Scout creature token that's all colors. That token gains haste until end of turn.

When Aridland Camaar enters the battlefield, create a 1/1 white Bird creature token with flying.

When Arisen Haploc enters the battlefield, return target creature card from a graveyard to its owner's hand.
Revive {5}{B}{B} ({5}{B}{B}, Exile this card from your graveyard: Create a token that's a copy of it except it has no mana cost. Revive only as a sorcery.)

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

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

Lifelink
When Army's Suppliers enters the battlefield, recruit. (Create a 0/0 white Soldier Army creature token, then put a +1/+1 counter on each Army you control.)

Trample
When Arpechian Bellowers enters the battlefield, harmonize. (Trigger up to one harmony of a permanent you control.)
Harmony — Search your library for a green creature card, reveal it, put it into your hand, then shuffle.

When Arpechian Groundskeeper enters the battlefield, rouse 1. (Put a +1/+1 counter on a permanent you control. If it isn't a creature, tap it and it becomes a 0/0 creature in addition to its other types.)
Remove a +1/+1 counter from Arpechian Groundskeeper: Draw a card.

When Arpechian Stag enters the battlefield, create a 3/3 red Elk creature token with haste, a 3/3 green Elk creature token with trample, and a 3/3 white Elk creature token with vigilance.

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

Enchant land
When Arrive, Surrounded by Petals enters the battlefield, audition for green. (Create a 1/1 Construct Actor creature token, a Scout Role giving 2/3 and vigilance, or a Warrior Role giving 3/2 and trample. Roles replace older ones.)
Enchanted land has “{T}: Add one mana of any color.”

When Arrogant Orator enters the battlefield, create a 0/1 black Cultist creature token with “{1}{B}{B}, Sacrifice three Cultists: Create a 5/5 black Demon creature token.”

When Artian, Phyrexian Architect enters the battlefield, search your library for a land card, put it onto the battlefield, then shuffle.
At the beginning of your upkeep, put a corruption counter on a land you control. Then create a 1/1 colorless Phyrexian artifact creature token for each land you control with a corruption counter on it.

When Artificial Wayfinder enters the battlefield, you may search your library for a basic land card, reveal it, put it into your hand, then shuffle.

When Artillery Mage enters the battlefield, it deals 5 damage to target creature you don't control.
{5}{R}, {T}, Discard a card: Artillery Mage deals 5 damage to target creature you don't control.

Flash
When Artisan of Marrow enters the battlefield, exile another target creature until Artisan of Marrow leaves the battlefield.

When Artisan's Genius enters the battlefield, you may tap three untapped artifacts or other enchantments you control. If you do, draw three cards.
{5}{W}{U}, Exile Artisan's Genius: Return any number of artifact or enchantment cards with different names from your graveyard to your hand.