msem-instigator

When Aerie Bell-Warden enters, if it's in a pack, you gain 5 life. (Two or more creatures you control with equal power are in a pack.)

Enchant creature
When Aerie Watch enters, draw a card.
Enchanted creature gets +1/+1 and has reach.

Vision (Whenever this or another creature you control enters, reveal the top card of your library. Then you may put that card into your graveyard.)
Whenever Aether Recoverer envisions a creature card, return target noncreature card from your graveyard to your hand.

When Ageless Weaver enters, create a green Aura enchantment token named Years of Experience attached to target creature. The token has enchant creature and “Enchanted creature gets +2/+2.”
Whenever an enchanted creature you control dies, create a 3/3 green Elemental creature token.

Improve {1} ({1}: Put a +1/+1 counter on this creature. This costs {1} more to activate for each +1/+1 counter on it. Improve only as a sorcery.)
Once each turn, when one or more counters are put on a permanent you control, create a 1/1 colorless Human creature token.
Whenever you attack with three or more creatures, destroy up to one target artifact or enchantment.

Whenever Agent of Vitu-Ghazi deals combat damage to a player, investigate. (Create a colorless Clue artifact token with “{2}, Sacrifice this artifact: Draw a card.”)

Target creature you control deals damage equal to its power to target creature you don't control.

Poisonous 1 (Whenever this creature deals combat damage to a player, that player gets a poison counter.)
At the beginning of your upkeep, destroy target artifact or enchantment if its controller is poisoned.

I, II — Search your library for a basic land card, reveal it, put it into your hand, then shuffle.
Discovery — {4}: You gain 2 life.

Enchant land
When Aid from Martoob enters, recruit. (Create a 0/0 white Soldier Army creature token, then put a +1/+1 counter on each Army you control.)
When enchanted land is tapped for mana, add one mana of any color.

Cast this spell only if creatures you control have a total power of 10 or greater or you control six or more lands.
Create two 6/6 green and white Elk creature tokens.

Move up to one +1/+1 counter from a creature you control to target creature you control. Then that creature fights target creature you don't control.

Trample
Other Hounds you control get +1/+1 and have trample.

Frenzy 2 (Whenever this creature attacks and isn't blocked, it gets +2/+0 until end of turn.)
Whenever Airam, Packleader becomes blocked, other creatures you control get +1/+1 until end of turn.

Melee (Whenever this creature attacks, it gets +1/+1 until end of turn for each opponent you attacked this combat.)
When Aith Aera Sentinel enters, create a 1/1 green Elf creature token.

Whenever a creature token you control enters, put a +1/+1 counter on target creature you control.

Trample
Wanderlust — Whenever Akkrixian Assailants attacks, if you control four or more differently named lands, put a +1/+1 counter on it.

Untap target creature. It gets +1/+1 for each token you control until end of turn.

When Alder Courtier dies, you gain 4 life.

Aleud Beastmaster has frenzy X, where X is the number of unblocked attacking creatures you control. (Whenever it attacks and isn't blocked, it gets +X/+0 until end of turn.)

Frenzy 1 (Whenever this creature attacks and isn't blocked, it gets +1/+0 until end of turn.)
Aleud Bladedancer has hexproof as long as it's attacking.

Enchant creature
Enchanted creature gets +2/+2 and has hexproof.
Sacrifice Aleud Grace: Enchanted creature gains indestructible until end of turn.

Frenzy 1 (Whenever this creature attacks and isn't blocked, it gets +1/+0 until end of turn.)
Whenever Aleud Pathfinder becomes blocked, untap up to two lands you control.

[+1]: Create a 1/1 green Saproling creature token. You gain 2 life.
[0]: Creature spells you cast this turn can't be countered. As they enter, they gain hexproof until your next turn.
[–2]: Create a green enchantment token named Survival with “You and other permanents you control have ward {1}.”

Search your library for a basic land card, put it onto the battlefield, then shuffle.
Crystallize. (Put a +1/+1 counter on a creature you control or create a Treasure.)