msem-instigator

Observation Field enters with three charge counters on it.
{2}, {T}, Remove a charge counter from Observation Field: Draw a card and gain 2 life.
{T}, Sacrifice Observation Field: Shuffle any number of target cards from your graveyard into your library.

Tribute 2 (As this creature enters, an opponent of your choice may put two +1/+1 counters on it.)
When Observing Guardian enters, if tribute wasn't paid, create a 2/2 white Cat creature token.

Put target nonland permanent on top of its owner's library. Create a Treasure token. (It's an artifact with “{T}, Sacrifice this artifact: Add one mana of any color.”)

When Occult Mastermind enters, create two 2/2 black Zombie creature tokens. When Occult Mastermind is no longer on the battlefield, sacrifice two Zombies.

Attacking creatures get -2/-0 until end of turn.
Metamorph {1}{U} (You may cast this card face down as a 2/2 creature for {3}. Turn it face up and cast it at any time for its metamorph cost.)

Slipstream (This creature can't be blocked as long as only creatures with slipstream are attacking.)
{T}: Salvage a creature card. (Exile one from your graveyard until this creature leaves the battlefield. Whenever this creature deals combat damage to a player, put a card it salvaged into your hand.)

Whenever one or more artifacts you control enter, put a +1/+1 counter on Octopus Shiny-Grabber and you gain 1 life.

Flash
When Odaya Magistrate enters, you may counter target noncreature spell.

Ode to the Red Wind deals 1 damage to target creature. It can't block this turn.
Showcase {3}{R} (Then if you cast this for its showcase cost, create a 1/1 red Bard creature token that can't block and exile this. Whenever it attacks, you may cast a free copy of this.)

Exile up to two target creatures controlled by different players. Return those creatures to the battlefield under their owners' control at the beginning of the next end step.

You may pay {R} and tap an untapped Warrior you control rather than pay this spell's mana cost.
Choose one —
• Double the power of target creature you control until end of turn.
• Target creature you control deals damage equal to its power to target creature or planeswalker.

Whenever you cast a spell, note its colors.
At the beginning of combat on your turn, up to X target creatures get +2/+0 and gain menace until end of turn, where X is the number of colors noted with Off-Set Rumormonger.

Destroy target artifact or enchantment. Scry 1. (To scry 1, look at the top card of your library. You may put that card on the bottom of your library.)

{T}: You may put a land card from your hand onto the battlefield.
{1}, {T}: Aetherize target land you control. (To aetherize, create a token that's a copy of it, then exile that token.)

You may cast Oil the Mind from your graveyard.
Target player mills three cards.
If Oil the Mind was cast from your graveyard, conjure a card named Fatigue and put it on top of your library. (It's a colorless sorcery that costs {2} with “Draw a card.”)

Target creature gets -X/-X until end of turn, where X is the number of enchantments you control.

{2}, {T}, Sacrifice Old Map: Search your library for a basic land card, put it onto the battlefield, then shuffle.

When Old Salt enters, forebode. (Create a tapped colorless Omen artifact token with “{T}, Discard a card, Sacrifice this artifact: Draw a card.”)

When Old-Oath Conviction enters or leaves the battlefield, create a 1/1 white Cleric creature token with lifelink.
{3}{B}, Sacrifice Old-Oath Conviction: Draw a card. Activate only as a sorcery.

Defender, flying
Menagerie — As long as there are five or more creature types among creatures you control, Old-Rune Sentinel can attack as though it didn't have defender.

Flying
Menagerie — When Old-Rune Watcher enters, if there are five or more creature types among creatures you control, draw a card.

Flying
When Old-World Forgotten dies, you may return target artifact or enchantment card from your graveyard to your hand.

Flying
At the beginning of your end step, untap target permanent you control.

Oldgrove Nurturer enters with a +1/+1 counter on it.
{G}, Remove a +1/+1 counter from a creature you control: Create a 1/1 colorless Construct artifact creature token.

Whenever you attack with one or more Pirates, create that many 1/1 white Bird creature tokens with flying that are tapped and attacking. At end of combat, choose one of those tokens, then exile the rest.