msem-instigator

Whenever Apostle of the Spirit Moon becomes blocked by a creature, Apostle of the Spirit Moon deals 1 damage to that creature and that creature's controller.

At the beginning of your upkeep, you may pay {1}{G/U}. If you do, proliferate. (Choose any number of permanents and/or players with counters on them, then give each another counter of each kind already there.)
At the beginning of your end step, you may pay {1}{G/U}. If you do, populate. (Create a token that's a copy of a creature token you control.)

Vigilance
If another creature would die, exile it instead.
At the beginning of your upkeep, return each creature card exiled with Arbiter of Endless Summer to the battlefield under its owner's control.

Wanderlust — When Ardent Explorers enters, 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 Arisen Haploc enters, 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.)

Whenever Arisen Helix attacks, scry 2.
If Arisen Helix would die, exile it instead.

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

Prevent all combat damage that would be dealt to Armored Axewarden as long as it's embattled. (A creature is embattled if it has a counter on it or a permanent you control attached to it.)

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.

Lands you control have hexproof.
{2}{G}{U}: Rouse 2. (Distribute two +1/+1 counters among permanents you control. If they aren't creatures, tap them and they become 0/0 creatures in addition to their other types.)

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.

Arsenal Curator gets +1/+1 as long as you control a Plains.
{2}{W}: Untap target creature you control. It gets +0/+1 until end of turn.

Flying
Clerics you control are Demons in addition to their other types.
Attacking Demons you control have deathtouch.

First mate — Twelve or more cards in your starting deck are Dragons or have “Dragon” in their printed rules text. (If this card outside the game is your chosen first mate, you may swap it with a card in your opening hand.)
Dragon spells you cast cost {1} less to cast.
Whenever Ashe attacks, it deals X damage to any target, where X is the number of Dragons you control.

Whenever Ashen Host becomes the target of a spell, Ashen Host deals 2 damage to any target.

{T}: Draw two cards. Starting with the next opponent in turn order, each opponent may discard a land card. The first to do so gains control of Ashen Mare. Activate only during your turn.

Trample
When Ashka Ritualist enters or whenever you cast a spell, if {R}{W} was spent to cast it, create two 1/1 red and green Warrior creature tokens. Put a +1/+1 counter on Ashka Ritualist.

Gestalt (When this or another creature enters under your control, you may merge it with the one in play, keeping counters and attachments. They become the permanent on top plus all abilities from under it.)
This creature can't be blocked by creatures with power 1 or less.

When Asking Imp enters, an opponent may pay 2 life. If they do, return Asking Imp to its owner's hand.

Flying, vigilance
Whenever a land you control enters, create a 2/2 green Ox creature token.
{3}{W}, Tap three untapped Oxen you control: Put a +1/+1 counter on each creature you control.

First strike
Chronicle (As this enters and after your draw step, add a lore counter. Stop after III.)
[Lore I-II] Put a +1/+1 counter on each of up to two other target creatures you control.
[Lore III] Remove all lore counters from Astral Capricine. Create two 0/1 white Goat creature tokens.

Menace
Chronicle (As this enters and after your draw step, add a lore counter. Stop after III.)
[Lore I-II] Exile the top card of your library. You may play that card this turn.
[Lore III] Remove all lore counters from
Astral Cerberus. It deals 3 damage to up to one target creature.

Deathtouch
Chronicle (As this enters and after your draw step, add a lore counter. Stop after III.)
[Lore I-II] You may sacrifice another creature. If you do, draw a card.
[Lore III] Remove all lore counters from Astral Leech. Each opponent sacrifices a creature.

Ward—Exile three cards from your graveyard. (Whenever this permanent becomes the target of a spell or ability an opponent controls, counter it unless that player exiles three cards from their graveyard.)
Menagerie — Astralhorn Familiar gets +2/+2 as long as there are five or more creature types among creatures you control.