msem-instigator

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.

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.”)

Whenever Arcane Duelist becomes tapped, target instant or sorcery card with mana value 1 in your graveyard gains flashback until end of turn. The flashback cost is equal to its mana cost. (You may cast that card from your graveyard for its flashback cost. Then exile it.)

Search your library for an instant or sorcery card, reveal it, put it into your hand, then shuffle.

Counter target spell.
Look at the top three cards of your library. Put one on top and the rest on the bottom in any order.

Arcane Sanctum enters tapped.
{T}: Add {W}, {U}, or {B}.

Harmony — Attach Arcane Saxophone to target creature.
When Arcane Saxophone enters, harmonize. (Trigger up to one harmony of one permanent you control.)
Equipped creature gets +2/+2.
Equip {4}

Whenever you cast a spell, draw a card if that spell has the same name as a card in your graveyard.

When Arcanomancer enters, return up to one target instant card and up to one target sorcery card from your graveyard to your hand.

You have no maximum hand size.
{T}: Add {C}.
{1}, {T}: Add one mana of any color.

{T}: Add {C}.
{2}, {T}, Sacrifice Arcor Diamond: Draw a card.

Create three 2/2 green Wolf creature tokens.

[+1]: Search your library for a land card, put it onto the battlefield, untap it, then shuffle. Sacrifice a land.
[–2]: Destroy target noncreature permanent. Its controller may search their library for a basic land card, put that card onto the battlefield, then shuffle.
[–6]: Return any number of land cards from your graveyard to the battlefield and untap them. They become 3/3 creatures with haste in addition to their other types.

Whenever Arena Challenger deals damage to a creature, upgrade it. (Give it one of the listed counters it doesn't already have.)
• +1/+1
• First strike
• Prowess

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.)

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.

Menace, haste
As long as Arleigh, Spellblade Prodigy is tapped, the first spell you cast during each other player's turn costs {U/R} less to cast. This effect reduces only the amount of colored mana you pay. (For example, if you cast a spell with mana cost {1}{R}, it costs {1} to cast.)

Flying
Whenever a creature you control phases in, it gains flying until end of turn.

Enchant creature
Enchanted creature gets +2/+2 and has trample.
Whenever enchanted creature deals damage, you gain that much life.

Target creature gains double strike 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.)

Whenever two or more creatures an opponent controls attack, adjudicate. (Create a white Aura enchantment token with enchant creature and “Sacrifice this token: Untap enchanted creature” attached to target creature.)
Enchanted creatures you control get +0/+2.

When Arms Merchant enters, 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.

When Army Guide dies, you may search your library for a basic land card, put it onto the battlefield tapped, then shuffle.
{2}{G}{W}, Sacrifice Army Guide: Exile target noncreature, nonland permanent. Activate only as a sorcery.