msem-instigator

Trample
Whenever Openmaw Demon or another Azra or Demon you control enters, you may exile target card from a graveyard.

Opera House enters tapped.
When Opera House enters, add one mana of any color.
{T}, Sacrifice Opera House: Search your library for a basic land card, put it onto the battlefield tapped, then shuffle.

Converge — When Operations Manager enters, create X 1/1 colorless Servo artifact creature tokens, where X is the number of colors of mana spent to cast Operations Manager.

Ophan Titan gets +3/+3 as long as there are no nonland cards in your graveyard.
Morph {1}{G} (You may cast this card face down as a 2/2 creature for {3}. Turn it face up any time for its morph cost.)

Lifelink (Damage dealt by this creature also causes you to gain that much life.)
When Ophelia's Neophyte enters, you may have another target creature you control gain lifelink until end of turn.

When Ophorio Scavenger enters, create an Idol token. (It's an artifact with “{1}, Sacrifice this artifact: Put a +1/+1 counter on target creature. Activate only as a sorcery.”)
Ophorio Scavenger gets +1/+1 as long as you control three or more artifacts.

{T}: Add {G}. If you control an attacking creature, add one mana of any color instead.

Voracious 2 (As this enters, you may sacrifice up to two artifacts and/or creatures. This creature enters with that many +1/+1 counters on it.)
When Opportunistic Beast enters, destroy up to one target creature that was dealt damage this turn.

Target creature gets -4/-4 until end of turn.
Civilized — Draw a card if you control an artifact, a creature, and an enchantment.

Enchant creature
Enchanted creature can't attack or block unless its controller pays {3}.
Activated abilities of enchanted creature cost {3} more to activate.

Creatures can't attack you unless their controller pays {3} for each of those creatures.

Scry 1.
Draw a card.

Whenever Optimistic Chronicler deals damage to a player or noncreature permanent, surveil 1, then draw a card.

Whenever you cast your first instant or sorcery spell each turn, create a Treasure token. (It's an artifact with “{T}, Sacrifice this artifact: Add one mana of any color.”)

When Opulent Proprietor enters, you may search your library and/or graveyard for an Aura, Aurashaper, Equipment, or Vehicle card, reveal it, and put it into your hand. If you search your library this way, shuffle.

Draw three cards, then discard two cards.

When Oracle Crab enters, scry 2. (To scry 2, look at the top two cards of your library, then put any number of them on the bottom of your library and the rest on top in any order.)

When Oracle of Edicts enters, adjudicate. (Create a white Aura enchantment token with enchant creature and “Sacrifice this token: Untap enchanted creature” attached to target creature.)
Whenever an Aura you control enters, scry 1.

Whenever Oracle of Flames becomes tapped, up to one target creature you control gets +2/-2 until end of turn.

Whenever you cast a spell during an opponent's turn, put a +1/+1 counter on Oracle of Tides.

Menace
At the beginning of your end step, if a player lost 3 or more life this turn, put a +1/+1 counter on target Azra or Demon you control.

Whenever you cast a noncreature spell, creatures you control get +1/+1 until end of turn.

Enchant creature
Enchanted creature gets -3/-3.
When enchanted creature dies, its controller may scry 1.

Each player mills three cards.
Draw a card.

Whenever you sacrifice an Idol, put a +1/+1 counter on Orchard Botanist.