msem-instigator

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

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

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.

When Arisen Troops dies, you may destroy target creature that was dealt damage this turn.

Trample
Whenever Arisen Tyrant attacks, mill three cards, then you may exile a card from your graveyard. You may cast a copy of the exiled card without paying its mana cost if the spell's mana value is 3 or less.
If Arisen Tyrant would die, exile it instead.

Enchant creature
Enchanted creature can't attack or block, and its activated abilities can't be activated.

Winnow (Damage dealt to this creature also causes you to lose that much life.)
{2}{B}: Each creature blocking Arroyo's Servant gains winnow until end of turn.

Once during each of your turns, when a card is put into a graveyard from anywhere, you may cast it. You may spend mana of any color to cast that spell.
When Arroyo, Infinitely Branching is put into your graveyard from anywhere, you may cast it.

{T}: Add {C}.
{5}, {T}, Sacrifice Ascendant's Cell: You may activate loyalty abilities of planeswalkers you control twice this turn rather than only once.

{T}: Add {C}.
{T}: Add one mana of any color. Activate only if you control a transformed permanent.

Whenever you cast a spell, put a burst counter on Ascending Downfall, then if that spell's mana value is less than the number of burst counters on Ascending Downfall, sacrifice it and it deals damage equal to the number of burst counters on it to any target.

Aspiring Dragon has flying and haste as long as you control another Dragon.
{2}{R}{R}: Aspiring Dragon gets +3/+0 until end of turn.

Vanguard — Whenever a creature you control attacks alone, it gets +1/+1 until end of turn.

Whenever a non-Spirit creature deals combat damage to a player, destroy that creature. Its controller creates a 1/1 colorless Spirit creature token.

When Atlas of Worlds enters, search your library for any number of land cards with different names and exile them, then shuffle.
You may play lands exiled with Atlas of Worlds.

Choose one or both —
• Prevent all combat damage that would be dealt to creatures this turn.
• Detain target creature. (Until your next turn, that creature can't attack or block and its activated abilities can't be activated.)

Attentive Glider gets +2/+2 and has flying as long as you cast an Adventure spell or a permanent you controlled explored this turn.

Enchant creature
As long as you control an untapped creature, enchanted creature can't attack or block.

You may put a creature card from your hand onto the battlefield. That creature gains haste until end of turn. Sacrifice that creature at the beginning of the next end step unless you pay its mana cost reduced by up to {3}{R}{R}.

Counter target spell. If you are glorious, draw a card. (You are glorious as long as you have a glory counter.)

Flash
When Augmented Spawn enters, create a 1/1 blue Merfolk creature token for each Island you control.
{U}, Sacrifice a Merfolk: Augmented Spawn gains hexproof until end of turn.

Whenever Aukashi, Electric Legacy enters or equipped creature dies, attach Aukashi to a creature you control.
Whenever equipped creature deals damage to a permanent or player, Aukashi deals 2 damage to that permanent or player.
Equipped creature has double strike as long as a creature you controlled died this turn.
Equip {2}

Whenever equipped creature deals combat damage to a player, exile an instant or sorcery card from your graveyard. Then copy any number of cards exiled with Aukashi, the Rising Storm with mana value X or less and cast the copies without paying their mana costs, where X is the number of cards exiled with Aukashi.
Equip {2}

Distorted (This creature can be blocked by tapped creatures but not untapped creatures.)
During each of your turns, you may cast an instant or sorcery spell from your graveyard. If that spell would be put into your graveyard, exile it instead.
Whenever Aurora, Soulweaver attacks, untap any number of target creatures.

Frenzy 2 (Whenever this creature attacks and isn't blocked, it gets +2/+0 until end of turn.)
Blocked creatures you control have first strike.