msem-instigator

{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}

When Mystic Mackerel enters, you may have target player mill two cards.
{3}{U}, Sacrifice Mystic Mackerel: Return target enchantment, instant, or sorcery card from your graveyard to your hand.

Whenever you cast a spell from exile, you may draw a card.
At the beginning of your upkeep, you may reveal the top card of your library.

When Mystic Seer enters, each player may scry 1.
{2}{U}: Draw a card, then discard a card.

Whenever a player casts a spell, that player exiles the top card of each library face down.
Each player may look at and play cards they exiled with Mystic of Many Winds.

Enchant creature
When Mystic's Mantle enters, draw a card.
Enchanted creature gets +1/+1.
Mirage {G} (You may cast this spell as though it had flash for its mirage cost. If you do, sacrifice it at the beginning of the next cleanup step.)

Each player mills three cards. For each instant and/or sorcery card milled this way, draw a card.

Reverberate {2}{G} (When you cast this spell, copy it if you paid its reverberate cost. The copy becomes a permanent when it resolves.)
Mystical Echo gets +1/+1 for each other Reflection you control.
Whenever you discard a card, Reflections you control gain trample until end of turn.

{T}: Mystical Elk becomes a copy of target creature card in your graveyard. Activate only as a sorcery. (It loses this ability.)

I, II — Look at the top four cards of your library. You may reveal a permanent card from among them and put it into your hand. Put the rest on the bottom of your library in a random order.
Discovery — At the beginning of your end step, you may put a permanent card from your hand onto the battlefield.

When Mythos Scribe enters, you may return target storied card from your graveyard to your hand. (Enchantments and legendary permanents are storied.)

[+1]: Reveal the top card of your library and put that card into your hand. You lose life equal to its mana value.
[0]: You gain 1 life for each card in your hand.
[–7]: Search your library for up to X cards, where X is the number of cards in your hand, and put them into your hand. Then shuffle.

You draw X cards and you lose X life, where X is the number of cards in your graveyard.

Stampede — Whenever Nacatl Skirmisher and a creature with greater power attack, creatures you control get +1/+0 until end of turn.
{R}, Sacrifice Nacatl Skirmisher: Destroy target artifact.

Haste
Whenever Nadei deals combat damage to a player, that player sacrifices a land. You may put a land card from a graveyard onto the battlefield under your control.

When Naga Cultivator enters, you may put a land card from your hand onto the battlefield.

{T}, Discard a card: Draw a card.

When Naiad of the Glen 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.”)
Naiad of the Glen has trample as long as it has a +1/+1 counter on it.

Flying
Whenever Naiala's Guide deals combat damage to a player, draw a card, then discard a card.