msem-instigator

Whenever you tap a land for mana, add one mana of any type that land produced.
Whenever you cast a spell with mana value greater than the number of lands you control, sacrifice a land.

Sacrifice a creature or discard a card: Exile the top card of target player's library. You may cast that card for as long as it remains exiled. Any player may activate this ability but only once each turn and only during their turn.
You and permanents you control have hexproof from spells that were exiled with Mr. Jackston or that share a name with a card exiled with Mr. Jackston.

At the beginning of your upkeep, if there are no noncreature cards in your graveyard, you may return target creature card from your graveyard to the battlefield.

Look at the top two cards of your library. Put one of them into your hand and the rest into your graveyard.
Rerun (If you cast this from your hand, exile it as it resolves. Whenever a creature you control dies, you may cast this card from exile without paying its mana cost.)

Enchant creature
Enchanted creature is a Horror with base power and toughness 3/3 and loses all other creature types and abilities.
Whenever enchanted creature deals combat damage to a creature, create a token that's a copy of Plagas Infestation and attach it to the damaged creature.

Flying
When Planchette Poltergeist enters the battlefield, you may exile target creature. Its owner may cast it from exile for as long as it remains exiled.

You may have Raging Reflection enter the battlefield as a copy of any creature on the battlefield, except it has “When this creature enters the battlefield, it fights another target creature that shares a name with it.”

Ravenous Attraction enters the battlefield with a +1/+1 counter on it.
Whenever a creature you control dies, double the number of each kind of counter on Ravenous Attraction.

Choose a creature. Exile the rest.

As an additional cost to cast this spell, sacrifice a noncreature permanent.
Search your library for a creature card with mana value equal to 1 plus the sacrificed permanent's mana value, put it onto the battlefield, then shuffle.

First strike
Whenever a creature dealt damage by Roadside Reaper this turn dies, you may discard a card. If you do, put a +1/+1 counter on Roadside Reaper and draw a card.

This spell costs {2} less to cast for each creature that died this turn.
Each player exiles all creature cards from their graveyard, then sacrifices each creature they control, then puts all creature cards they own exiled this way onto the battlefield. Exile Sea of Corpses.

Discard your hand. Draw cards equal to the number of creatures that died this turn.

Spells your opponents cast that target Sheltered Snowman cost {2} more to cast.
Whenever you cast a spell from exile, put a +1/+1 counter on Sheltered Snowman. It can't be blocked this turn.

You may have Snowfield Doppelganger enter the battlefield as a copy of any creature on the battlefield, except it has “While a player is choosing targets as part of casting a spell, that player must choose at least one other creature that shares a name with this creature if able.”

Look at the top five cards of your library. You may reveal a nonland card from among them. If you do, put that card into your hand and cast a copy of it without paying its mana cost. Put the rest into your graveyard.

Choose one or more —
• Counter target activated ability or triggered ability.
• Prevent all combat damage that would be dealt this turn.

At the beginning of each player's upkeep, that player discards a card. If that player has no cards in hand, instead they sacrifice a permanent. If they control no permanents, instead they lose the game.

Menace
Discard a creature card or sacrifice a creature or exile a creature card from your graveyard: Put a +1/+1 counter on Starving Stalker. Activate only once each turn.

Subway Shambler can't be blocked by creatures with lesser power.
At the beginning of each end step, if you're horrific, put a +1/+1 counter on Subway Shambler. (You're horrific as long as you've sacrificed a permanent or discarded a card this turn.)

Sunken Homestead enters the battlefield tapped.
{T}: Add {B}.
{2}{B}: Until end of turn, Sunken Homestead becomes a 2/2 Zombie creature with “When this creature dies, return it to the battlefield.” Activate only if you're horrific.

At the beginning of each end step, create X 1/1 white Spirit creature tokens with flying, where X is the number of nontoken creatures that died this turn.

Instant and sorcery spells you control have rerun. (Exile the spell as it resolves if you cast it from your hand. Whenever a creature you control dies, you may cast that card from exile without paying its mana cost.)