msem-instigator

As The Mistake enters, choose a card name.
Activated abilities of sources with the chosen name can't be activated unless they're mana abilities.
Unveil {5} ({5}: Transform this. Unveil only as a sorcery.)

[+1]: Add {W}{U}{B}{R}{G}.
[–1]: Exile the top three cards of your library. Until end of turn, you may play cards exiled with this permanent.
[–3]: Create a 5/5 Archon creature token that's all colors and has flying and “When this creature enters, it deals 5 damage to any target.”

Creatures you control have trample, haste, and hexproof.
{2}{G}{G}: Create a 2/2 white Cat creature token.

At the beginning of your upkeep, return target creature card from your graveyard to the battlefield.

Create a 1/1 white Spirit creature token with flying. (Then exile this card. You may cast the artifact later from exile.)

Permanent cards in your graveyard have The Undercity Amalgam's Adventure.
Once during each of your turns, you may cast an Adventure spell from your graveyard.

The Urchin King's power and toughness are each equal to the number of cards in all graveyards.
Sacrifice a creature: The Urchin King gains lifelink and indestructible until end of turn.

Target creature gets +2/+0 and gains haste until end of turn.
Fabled {2}{R} (Then if you cast this for its fabled cost, put it onto the battlefield transformed attached to that creature.)

Each creature you control enters with an additional +1/+1 counter on it.
Each planeswalker you control enters with an additional loyalty counter on it.

Experience (Whenever this creature attacks, if it has fewer than three +1/+1 counters on it, put a +1/+1 counter on it.)
When Tidepool Turtle has three or more +1/+1 counters on it, remove them all and transform it.

Untap target land. Scry 1. (To scry 1, look at the top card of your library. You may put that card on the bottom of your library.)
Fabled {3}{G}{G} (Then if you cast this for its fabled cost, put it onto the battlefield transformed attached to that land.)

Take an extra turn after this one. Exile Time if it wasn't fused.
Fuse (You may cast one or both halves of this card from your hand.)

Tap target creature. If you control a Monk, draw a card. (Then exile this card. You may cast the creature later from exile.)

Flying

Tinyvale Treetops enters tapped unless you played it from exile.
{T}: Add {G} or {W}.

{3}, Sacrifice Titanic Fossil: Mill three cards, then you may exile a card from your graveyard. You may cast a copy of the exiled card without paying its mana cost if the spell's mana value is 3 or less. Activate only as a sorcery.
{3}{U}{B}: Return Titanic Fossil from your graveyard to the battlefield transformed. Activate only during your turn.

Return target permanent you control to its owner's hand. (Then exile this card. You may cast the creature later from exile.)

At the beginning of each end step, put a +1/+1 counter on equipped creature for each creature that died this turn.
Equip {1}

Chosen one ({W}{U}{B}{R}{G}: Transform this permanent.)
When Tomb Steward enters, search your library for a card and put it into your graveyard. Then shuffle.

Ward {2}
Even numbered spells you cast each turn costs {2} less to cast. (The second, fourth, sixth, etc.)

Enchant creature
Enchanted creature gets +3/+3 and has trample.

Target creature can't be blocked this turn. Scry 1.
Fabled {2}{U} (Then if you cast this for its fabled cost, put it onto the battlefield transformed attached to that creature.)

Whenever Toxic Miscreant deals combat damage to a player, that player discards a card.

Search your library for a creature card, reveal it, then shuffle and put that card second from the top.

Draw a card. (Cast a copy of this spell once while this creature is on the battlefield.)