msem-instigator

Enchant opponent
Whenever you attack enchanted player, look at the top X cards of your library, where X is one plus the number of attacking creatures you control. Put one of those cards into your hand and the rest on the bottom of your library in any order.

Target creature gets +3/+3 until end of turn.
Cycling {2} ({2}, Discard this card: Draw a card.)

When Smoldering Husk dies, it deals 2 damage to any target.
{2}{R}: Smoldering Husk gets +2/+0 until end of turn.

Enchant artifact or creature
Enchanted permanent doesn't untap during its controller's untap step.
Whenever you make first contact, scry 1. (You make first contact the first time each turn you cast a spell with a name not in your graveyard or control already.)

Target creature gets -X/-X until end of turn, where X is the number of cards in your graveyard. If that creature would die this turn, exile it instead.
Cycling {B} ({B}, Discard this card: Draw a card.)

First strike

When Somnambulance enters, each player conjures a card named Fatigue and puts it on top of their library. (It's a colorless sorcery that costs {2} with “Draw a card.”)
Whenever a player casts a spell named Fatigue, you may draw a card. If you do, you lose 1 life.

Put three +1/+1 counters on target creature you control. It voyages. (If it isn't blocking or targeted by another spell or ability, it phases out.)

Spend only black mana on X.
Any number of target players each draw X cards and lose X life.

Spare Supplies enters tapped.
When Spare Supplies enters, draw a card.
{2}, {T}, Sacrifice Spare Supplies: Draw a card.

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

Gestalt (When this or another creature enters under your control, you may merge it with the one in play, keeping counters and attachments. They become the permanent on top plus all abilities from under it.)
If you would gain life, you may put a +1/+1 counter on this creature instead.
When this creature has toughness 20 or greater, you win the game.

When Speaker of Open Waters enters, create a green and white Aura enchantment token named Moray's Resolve attached to target creature you control. The token has enchant creature and “Enchanted creatures you control get +2/+2 and have trample and lifelink.”

When Specimen Collector enters, you may 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.)

Haste
Whenever Spellslinger Elf deals combat damage to a player, draw a card, then you may cast a card from your hand with mana value 3 or less without paying its mana cost.

Whenever you draw a card, put a dream counter on Stargazing.
Remove seven dream counters from Stargazing and exile it: Shuffle your hand and graveyard into your library, then draw seven cards.

{T}: Add {C}.
{2}, Pay 2 life: Starved Oasis becomes a 4/2 Elemental creature until end of turn. It's still a land.

{G}, Discard a card: Staunch Constrictor gets +1/+1 until end of turn.

Stinging Swordfish has first strike as long as it's attacking.
When Stinging Swordfish dies, create an Equipment enchantment artifact token named Fish Sword with “Equipped creature gets +3/+1,” “Equipped creature has first strike as long as it's attacking,” and equip {2}. You may attach that token to a creature you control.

Mill five cards, then for each of those cards, a creature you control salvages that card unless an opponent pays 3 life. (Exile it from your graveyard until that creature leaves the battlefield. Whenever that creature deals combat damage to a player, put a card it salvaged into your hand.)

Search your library for two basic land cards and put them onto the battlefield tapped. Then they become 0/1 green Plant creatures with “This creature can't block” in addition to their other colors, types, and abilities.

Enchant opponent
At the beginning of enchanted player's upkeep, they mill two cards.
{U}, Sacrifice Strange Tides: Shuffle up to four target cards from your graveyard into your library.

Concord — At the beginning of combat on your turn, if there are four or more card types among permanents you control, Sturdyshell Hammerclaw gets +2/+1 and gains trample until end of turn.

When Stygian Leviathan enters, target opponent loses life equal to the number of Curses attached to them and you gain that much life.

This spell costs {1} less to cast for each Horror you control.
Exile up to one target non-Horror creature.
Coalesce {7}{W} (You may cast this from your graveyard for {7}{W}. If you do, it enters as a Horror creature after it resolves. Exile it if it would leave the battlefield or not resolve.)