msem-instigator

Counter target spell. Draw a card, then discard a card.

Target creature gets +2/+2 until end of turn. If it's an enchanted creature or enchantment creature, it also gains hexproof and indestructible until end of turn. (It can't be the target of spells or abilities your opponents control. Damage and effects that say “destroy” don't destroy it.)

As Aquatic Refuge enters, you may tap an untapped creature you control. If you don't, Aquatic Refuge enters tapped.
{T}: Add {W} or {U}.

{U}: Aqueous Treader gets +1/-1 until end of turn.
{U}: Aqueous Treader gets -1/+1 until end of turn.

Other creatures you control can't attack or block alone.

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.)

Flying, lifelink
Improve {1}{W/B} ({1}{W/B}: 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 you gain life, you may have each opponent lose 2 life.

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

Whenever Aravant Smuggler deals combat damage to an opponent, if it's embattled, draw a card. (A creature is embattled if it has a counter on it or a permanent you control attached to it.)

{1}{R}: Aravant Throatcutter and up to one other target Pirate or Rogue you control each get +1/+0 until end of turn.

Equipped creature gets +2/+2.
Whenever equipped creature deals combat damage to a player, exile cards from the top of their library until they exile a nonland card. You may cast that card without paying its mana cost.
Equip {2}

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

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.)

Flying
When Arbiter of Silence enters, exile all other creatures until Arbiter of Silence leaves the battlefield. (They return to the battlefield under their owners' control.)

{2}{B}, Sacrifice a creature: Draw a card. You gain 1 life.

Flash
Flying
As long as an opponent controls more creatures than you, Arbiter of the Scales gets +2/+2 and has first strike and lifelink.

This spell costs {1} less to cast for each differently named land you control.
Reach, trample

Trample
When Arborback Stomper enters, you gain 5 life.

As long as Arboreal Runes is on the battlefield or in your graveyard, it's a Forest land in addition to its other types.
{T}: Add one mana of any color.

Flash
Enchant creature
When Arcane Anesthesia enters, tap enchanted creature.
Enchanted creature doesn't untap during its controller's untap step.

Counter target spell. If a permanent spell is countered this way, create a Gold token. (It's an artifact with “Sacrifice this artifact: Add one mana of any color.”)

Activated abilities of artifacts cost {2} more to activate.

Enchant creature
Enchanted creature gets +1/+1 and has flying and prowess.

Prowess
When Arcane Dredger enters, return target instant or sorcery card from your graveyard to your hand.