msem-instigator

Until end of turn, creatures you control get +1/+1 and creatures your opponents control get -1/-1.

Whenever you cast an instant or sorcery spell, upgrade Error Exploiter. (Give it one of the listed counters it doesn't already have.)
• +1/+1
• Flying
• Hexproof

Put two +1/+1 or loyalty counters on target creature or planeswalker. It gains lifelink until end of turn.

You draw two cards, lose 2 life, and create a Gold token. (It's an artifact with “Sacrifice this artifact: Add one mana of any color.”)

Whenever Tide Crasher attacks, if you control another Merfolk, tap target creature defending player controls.

Flying
When Bogsnatcher Drake enters, create a colorless artifact token named Lotus Petal with “{T}, Sacrifice this artifact: Add one mana of any color.”

Target creature gets -2/-2 and is marked until end of turn.

Trample
You may spend black and green mana as though it were mana of any color.
Whenever Closing-Act Abomination attacks, look at the top X cards of your library, where X is the number of colors among cards in your graveyard. Put up to one of them into your hand and the rest on the bottom of your library in a random order.

Basic lands you control have all basic land types.
Augmented — Whenever you cast an instant or sorcery spell, if you've spent {W}{U}{B}{R}{G} to cast spells this turn, copy it. You may choose new targets for the copy.

Other creatures you control can't attack or block alone.

Flying
Melee (Whenever this creature attacks, it gets +1/+1 until end of turn for each opponent you attacked this combat.)

Transcend (Activate as a sorcery to gain the next type and a +1/+1 counter.)
Menace
{2}{B}: Demigod — Surveil 2. Each opponent loses 2 life and you gain 2 life.
{4}{B}: God — Search your library for two cards with different names and reveal them. An opponent chooses one. Put the chosen card into your graveyard and the rest into your hand. Then shuffle.

Enchant creature
Enchanted creature gets +1/+0 and can't be blocked by creatures with greater mana values.

Target creature you control fights another target creature.
Inscribe {3}{G} ({3}{G}: Exile this card from your hand inscribed on a creature you control. Whenever that creature attacks, its controller may cast a copy of the inscribed card without paying its mana cost. Inscribe only as a sorcery.)

Whenever you cast an artifact or enchantment spell, scry 1, then create a 1/1 white Merfolk creature token.
Whenever you cast a Merfolk spell, look at the top card of your library. If it's an artifact or enchantment card, you may reveal it and put it into your hand.

Flying
Wither (This deals damage to creatures in the form of -1/-1 counters.)

When you cast this spell from your hand, return it to your hand.
Choose one —
• Stormcalling deals 4 damage to any target.
• Exile target artifact.

As an additional cost to cast this spell, reveal a sorcery card from your hand or pay {2}.
Return target card from your graveyard to your hand.

When Festering Shipwreck enters, create a Vial token. (It's an artifact with “{1}, Sacrifice this and another permanent: Draw a card. Activate only during your turn.”)
At the beginning of each player's upkeep, that player sacrifices a nonland permanent.

Vanishing 2 (This permanent enters with two time counters on it. At the beginning of your upkeep, remove a time counter from it. When the last is removed, sacrifice it.)
{T}: Add {C}.
When Unstable Footing is put into your graveyard from the battlefield, if it had no time counters on it, search your library for a basic land card, put it onto the battlefield, then shuffle.

Whenever a permanent enters under an opponent's control, reveal the top card of your library. If it's a permanent card that shares a type with that permanent, you may put it onto the battlefield. Otherwise, put it on the bottom of your library.

This spell costs {1} less to cast for each permanent you control that's a Dragon or a Hound.
Flying, haste
Whenever Gold Retriever attacks, abound. (You may cast a nonland card that costs less than this from your hand without paying its mana cost.)

Whenever you gain life, put a +1/+1 counter on Wayfaring Pilgrim.

Concentrated Blast deals 5 damage to target creature.