msem-instigator

{T}: Put a luster counter on Object of Awe.
{1}{R}, {T}: Discard up to X cards, then draw a card for each card discarded this way. X is the number of luster counters on Object of Awe.
{3}{R}: Until end of turn, Object of Awe becomes an X/X red Phoenix creature with flying, where X is the number of luster counters on Object of Awe.

Whenever a creature enters, destroy it unless its controller pays 3 life.

Obliterating Blast deals 3 damage to any target. A creature dealt damage this way this turn can't be regenerated this turn. If that creature would die this turn, exile it instead.

Target opponent exiles a card from their hand. Scry 2.
Tether (Then if you cast this from your hand, you may exile it tethered to a creature you control. When it dies, you may cast this from exile without paying its mana cost.)

Obscoriate deals 4 damage to target creature or planeswalker. The next time that permanent would die this turn, instead put a basalt counter on it, it becomes a Mountain land named Charred Remains, loses all other card types, and gains “At the beginning of your upkeep, Charred Remains deals 1 damage to you.” (It has “{T}: Add {R}” and loses abilities it already had.)

When Obscure Apostle 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.”)
Whenever you sacrifice an Idol, Obscure Apostle can't be blocked this turn.

Return target creature to its owner's hand.
Concord — If there are four or more card types among permanents you control, draw a card.

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.

This spell costs {1} less to cast for each artifact and/or enchantment you control.
Trample
{1}, Sacrifice another cryptic permanent you control or exile a cryptic card from your graveyard: Put a +1/+1 counter on Observer of Aeons. (Artifacts, enchantments, and modal spells are cryptic.)

Flash
Whenever you cast an artifact or enchantment spell, put a +1/+1 counter on Observer of Secret Paths. It can't be blocked this turn.

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.

Other creatures you control get +2/+0.
Creatures your opponents control get -1/-1.
Fleeting {2}{B} (You may cast this spell for its fleeting cost. If you do, sacrifice it at the beginning of the next end step.)

Whenever you attack, you may double target attacking creature's power. If you do, sacrifice it at the beginning of the next step.
Whenever one or more red creatures you control enter, creatures you control get +1/+0 and gain trample until end of turn.

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.

Tithe (As you cast this spell, you may tap three artifacts and/or creatures you control.)
Search your library for a card and put that card into your hand, then shuffle. If this spell's tithe was paid, add {B}{B}{B}{B}.

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.)

Flash
Ocean's Edge Kraken enters with a hexproof counter on it.
{6}{U}{U}, Remove a hexproof counter from Ocean's Edge Kraken: Return all other creatures to their owners' hands.

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.)

Motley — At the beginning of combat on your turn, if there are five or more names among nonland permanents you control, Ochre Knight gets +2/+1 until end of turn and you gain 1 life.

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.

Deception {2}{U} ({2}{U}, Return an unblocked attacker you control to hand: Put this card onto the battlefield from your hand tapped and attacking.)
Whenever a creature you control deals combat damage to an opponent, you may draw a card.

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.)

Slipstream (This creature can't be blocked as long as only creatures with slipstream are attacking.)
Concord — Once each turn, when an opponent casts a spell or activates an ability that targets a Merfolk or enchantment you control, you may counter that spell or ability if there are four or more card types among permanents you control.