Humongulus

Hexproof (This creature can't be the target of spells or abilities your opponents control.)

Case of the Lost Witness

When this Case enters, conjure four cards named Fblthp, the Lost into your library, then shuffle. Draw a card.
To solve — You control a legendary Homunculus.
Solved — You may look at the top card of your library any time and you may play lands and cast spells from the top of your library.

Well of Lost Dreams

Whenever you gain life, you may pay {X}, where X is less than or equal to the amount of life you gained. If you do, draw X cards.

Repulsive Mutation

Put X +1/+1 counters on target creature you control. Then counter up to one target spell unless its controller pays mana equal to the greatest power among creatures you control.

Frantic Search

Draw two cards, then discard two cards. Untap up to three lands.

Fierce Guardianship

If you control a commander, you may cast this spell without paying its mana cost.
Counter target noncreature spell.

Fblthp, the Lost

When Fblthp enters, draw a card. If it entered from your library or was cast from your library, draw two cards instead.
When Fblthp becomes the target of a spell, shuffle Fblthp into its owner's library.

Path to Exile

Exile target creature. Its controller may search their library for a basic land card, put that card onto the battlefield tapped, then shuffle.

Wayfarer's Bauble

{2}, {T}, Sacrifice this artifact: Search your library for a basic land card, put that card onto the battlefield tapped, then shuffle.

Jeering Homunculus

When this creature enters, you may goad target creature. (Until your next turn, that creature attacks each combat if able and attacks a player other than you if able.)

Lightning Bolt

Lightning Bolt deals 3 damage to any target.

Delayed Blast Fireball

Delayed Blast Fireball deals 2 damage to each opponent and each creature they control. If this spell was cast from exile, it deals 5 damage to each opponent and each creature they control instead.
Foretell {4}{R}{R} (During your turn, you may pay {2} and exile this card from your hand face down. Cast it on a later turn for its foretell cost.)

Seasonal Sequels

Pitch the titles of up to X holiday-themed sequels to target spell. Copy that spell for each title pitched, except the copy has that name. You may choose new targets for the copies. (Simply adding numbers isn't festive enough.)

The Grand Tour

Exile target permanent, then put it into its owner's hand. That player discards that card, then puts it on top of their library. Then they put it onto the battlefield.

Mana Geyser

Add {R} for each tapped land your opponents control.

They Went This Way

Search your library for a basic land card, put it onto the battlefield tapped, then shuffle. Investigate. (Create a Clue token. It's an artifact with "{2}, Sacrifice this token: Draw a card.")

Crime Novelist

Whenever you sacrifice an artifact, put a +1/+1 counter on this creature and add {R}.

Borborygmos and Fblthp

Whenever Borborygmos and Fblthp enters or attacks, draw a card, then you may discard any number of land cards. When you discard one or more cards this way, Borborygmos and Fblthp deals twice that much damage to target creature.
{1}{U}: Put Borborygmos and Fblthp into its owner's library third from the top.

Shelldock Isle

Hideaway 4 (When this land enters, look at the top four cards of your library, exile one face down, then put the rest on the bottom in a random order.)
This land enters tapped.
{T}: Add {U}.
{U}, {T}: You may play the exiled card without paying its mana cost if a library has twenty or fewer cards in it.

Defender of the Queue

Positioning (As this creature enters, lock your creatures in order from left to right for as long as you control a creature with positioning. Each time a creature enters or comes under your control, position it to the left or right of another creature you control.)
Adjacent creatures to the left and right of Defender of the Queue get +1/+1 and have vigilance.

Super-Duper Lost

Put target creature into its owner's library just beneath the top X cards of that library, where X is the number of doors you can see from your seat.

Voidslime

Counter target spell, activated ability, or triggered ability. (Mana abilities can't be targeted.)

Who // What // When // Where // Why

Offender at Large

Disguise {4}{R} (You may cast this card face down for {3} as a 2/2 creature with ward {2}. Turn it face up any time for its disguise cost.)
When this creature enters or is turned face up, up to one target creature gets +2/+0 until end of turn.

Coveted Jewel

When this artifact enters, draw three cards.
{T}: Add three mana of any one color.
Whenever one or more creatures an opponent controls attack you and aren't blocked, that player draws three cards and gains control of this artifact. Untap it.

Captive Audience

This enchantment enters under the control of an opponent of your choice.
At the beginning of your upkeep, choose one that hasn't been chosen —
• Your life total becomes 4.
• Discard your hand.
• Each opponent creates five 2/2 black Zombie creature tokens.

Fblthp: Completely, Utterly, Totally Lost

When you planeswalk to this plane and at the beginning of your upkeep, create a Map token. (It's an artifact with "{1}, {T}, Sacrifice this token: Target creature you control explores. Activate only as a sorcery.")
Whenever chaos ensues, draw two cards, then discard two cards. Untap up to three lands.

Riverpyre Verge

{T}: Add {R}.
{T}: Add {U}. Activate only if you control an Island or a Mountain.

Totally Lost

Put target nonland permanent on top of its owner's library.

Unquestioned Authority

Enchant creature
When this Aura enters, draw a card.
Enchanted creature has protection from creatures.

Statute of Denial

Counter target spell. If you control a blue creature, draw a card, then discard a card.

March of the Multitudes

Convoke (Your creatures can help cast this spell. Each creature you tap while casting this spell pays for {1} or one mana of that creature's color.)
Create X 1/1 white Soldier creature tokens with lifelink.

Intruder Alarm

Creatures don't untap during their controllers' untap steps.
Whenever a creature enters, untap all creatures.

Familiar Beeble Mascot

{TK}{TK} — Whenever this creature attacks, untap target permanent.
{TK}{TK}{TK}{TK} — Whenever a creature enters under your control, creatures you control get +1/+1 until end of turn.
{TK}{TK} — 2/3
{TK}{TK}{TK} — 5/3

Fblthp, Lost on the Range

Ward {2}
You may look at the top card of your library any time.
The top card of your library has plot. The plot cost is equal to its mana cost.
You may plot nonland cards from the top of your library.

Solve the Equation

Search your library for an instant or sorcery card, reveal it, put it into your hand, then shuffle.

Karlov Watchdog

Vigilance
Permanents your opponents control can't be turned face up during your turn.
Whenever you attack with three or more creatures, creatures you control get +1/+1 until end of turn.