msem-instigator

At the beginning of your upkeep, germinate. Then if creatures you control have total power 10 or greater, transform Mushroom Merchant. (To germinate, put a +1/+1 counter on a creature or create a 1/1 green Saproling creature token.)

Counter target enchantment, instant, or sorcery spell. (Then exile this card. You may cast the creature later from exile.)

Put a +1/+1 counter on up to one target creature. (Then exile this card. You may play the land later from exile.)

Create two 1/1 white Soldier creature tokens. Prevent all damage that would be dealt to them this turn.

{T}: Add {C}.
Whenever Mustering Grounds becomes tapped, if it's enchanted, you may pay {2}. If you do, create a 1/1 white Soldier creature token with vigilance.

You may have Mutalithic Golem enter as a copy of any land on the battlefield, except it's an artifact in addition to its other types.

First strike
When Mutilated Warrior enters, you may have it deal damage to each player equal to the number of Warriors you control.

Whenever a creature you control dies, destroy target creature you don't control.

Menace
Other attacking Hounds you control get +2/+0.

Reveal cards from the top of your library until you reveal a creature card and a land card. Put those cards into your hand and the rest on the bottom of your library in a random order.
Concord — If there are four or more card types among permanents you control, create two Treasure tokens.

Equipped creature gets +2/+2.
Concord — Whenever equipped creature attacks, if there are four or more card types among permanents you control, create a 3/3 red Shark enchantment creature token that's tapped and attacking. Exile that token at the beginning of the next end step.
Equip {1}

[+1]: Create a tapped colorless artifact token named Conch Shell with “{T}: Add one mana of any color. Spend this mana only to cast permanent spells.”
[–1]: Reveal the top X cards of your library, where X is the number of card types among permanents you control. Put a permanent card from among them into your hand and the rest into your graveyard.
[–3]: Create two 3/3 red Shark enchantment creature tokens.

Whenever Mysteries of Life enters or you create a token, choose one that hasn't been chosen this turn —
• You gain 2 life.
• Draw a card, then discard a card.
• You may tap or untap target permanent.

Whenever a card is put into a graveyard this turn, you may put it on the bottom of its owner's library.
Draw a card.

Return a permanent you control to its owner's hand.
Investigate. (Create a colorless Clue artifact token with “{2}, Sacrifice this artifact: Draw a card.”)

As Mysterious Cataract enters, you may pay 2 life. If you don't, Mysterious Cataract enters tapped.
{T}, Sacrifice Mysterious Cataract: Search your library for a Forest or Island card, put it onto the battlefield, then shuffle.

{X}, Exile Mysterious Coffer: Return all nonland permanents with mana value X or less to their owner's hands.

Choose one —
• Return target artifact or enchantment card from your graveyard to your hand.
• Return target creature card with mana value 2 or less from your graveyard to your hand.
Cycling {2} ({2}, Discard this card: Draw a card.)

{T}: Add {C}. Spend this mana only to cast a creature spell with a creature type no creature you control has.

(As you complete a condition, decode it. After all are decoded, you solve the mystery and transform this.)
When Mystery of the Crashed Craft enters, create two 1/1 red Alien creature tokens with “This creature can't block.”
{MG}—You cast an instant spell.
{MG}—You cast a sorcery spell.

(As you complete a condition, decode it. After all are decoded, you solve the mystery and transform it.)
When Mystery of the Dying Herds enters, create a 0/2 white Ox creature token.
A creature you control dies.
You have 4 or more life than your starting life total.

Search your library for up to two cards with different names and reveal them. Target opponent chooses one of those cards. Put the chosen card into your graveyard and the rest into your hand. Then shuffle.

{T}: Add one mana of any color. If that mana is spent on a legendary creature spell, it enters with an additional +1/+1 counter on it.

Create a token that's a copy of target creature, except its power and toughness are switched. Sacrifice that token at the beginning of your next end step.

Equipped creature gets +1/+1.
Equip {1}