Form of the Squirrel

As Form of the Squirrel enters, create a 1/1 green Squirrel creature token. You lose the game when that creature leaves the battlefield.
Creatures can't attack you.
You have shroud.
You can't cast spells.

Farewell to Arms

As Farewell to Arms enters, choose a hand attached to an opponent's arm.
When the chosen hand isn't behind its owner's back, sacrifice Farewell to Arms. If you do, that player discards their hand . . . of cards. (The lawyers wouldn't let us do it the other way.)

Enter the Dungeon

Players play a Magic subgame under the table, starting at 5 life and using their libraries as their decks. The winner searches their library for two cards, puts those cards into their hand, then shuffles.

Incoming!

Each player searches their library for any number of artifact, creature, enchantment, and/or land cards, puts them onto the battlefield, then shuffles.

Krark's Other Thumb

If you would roll a die, instead roll two of those dice and ignore one of those results.

Rock Lobster

Creatures named Scissors Lizard can't attack or block.

City of Ass

City of Ass enters tapped.
{T}: Add one and one-half mana of any one color.

Mana Screw

{1}: Flip a coin. If you win the flip, add {C}{C}. Activate only as an instant.

S.N.O.T.

You may have S.N.O.T. enter stuck to another creature named S.N.O.T. If you do, all those creatures form a single creature.
S.N.O.T.'s power and toughness are each equal to the square of the number of cards named S.N.O.T. stuck together to form it. (One is a 1/1, two are a 4/4, three are a 9/9, and four are a 16/16. If you manage to get -1 S.N.O.T.s stuck together, it's a 1/1.)

Paper Tiger

Creatures named Rock Lobster can't attack or block.

Entirely Normal Armchair

During your turn, if Entirely Normal Armchair is in your hand, you may hide it on the battlefield.
{0}: Return Entirely Normal Armchair to its owner's hand. Only your opponents may activate this ability and only if they see Entirely Normal Armchair.
{2}, Sacrifice Entirely Normal Armchair: Destroy target attacking creature.

Atomwheel Acrobats

Whenever you roll a 1 or 2, put that many +1/+1 counters on Atomwheel Acrobats.
{2}{G}: Roll a six-sided die.

Stone-Cold Basilisk

Whenever Stone-Cold Basilisk blocks or becomes blocked by a creature with fewer letters in its name, destroy that creature at end of combat. (Punctuation and spaces aren't letters.)
Whenever an opponent reads Stone-Cold Basilisk, that player is turned to stone until end of turn. Stoned players can't attack, block, cast spells, or activate abilities.

Inhumaniac

At the beginning of your upkeep, roll a six-sided die. On a 3 or 4, put a +1/+1 counter on Inhumaniac. On a 5 or higher, put two +1/+1 counters on it. On a 1, remove all +1/+1 counters from Inhumaniac.

Elvish House Party

Elvish House Party's power and toughness are each equal to the current hour, using the twelve-hour system.

Forest

Letter Bomb

When Letter Bomb enters, sign it and shuffle it into target player's library. That player reveals each card they draw until they draw Letter Bomb. When that player draws Letter Bomb, it deals 19½ damage to them.

Shoe Tree

Shoe Tree enters with up to two shoe counters on it. Use your shoes as counters.
Shoe Tree gets +1/+1 for each shoe counter on it.

The Fallen Apart

The Fallen Apart enters with two arms and two legs.
Whenever damage is dealt to The Fallen Apart, remove an arm or a leg from it.
The Fallen Apart can't attack if it has no legs and can't block if it has no arms.

Swamp

Kill! Destroy!

Destroy target nonblack creature.
Gotcha — If an opponent says "kill" or "destroy," you may say "Gotcha!" When you do, return Kill! Destroy! from your graveyard to your hand.

Scissors Lizard

Creatures named Paper Tiger can't attack or block.

Land Aid '04

Search your library for a basic land card, put that card onto the battlefield tapped, then shuffle. If you sang a song the whole time you were searching and shuffling, you may untap that land.

B-I-N-G-O

Trample
Whenever a player casts a spell, put a chip counter on its mana value.
B-I-N-G-O gets +9/+9 for each set of three numbers in a row with chip counters on them.

Granny's Payback

As Luck Would Have It

Hexproof
Whenever you roll a die, put a number of luck counters on As Luck Would Have It equal to the result. Then if there are 100 or more luck counters on As Luck Would Have It, you win the game. (Count both rolls if you reroll a die.)

Gerrymandering

Exile all lands. Give each player a number of those cards chosen at random equal to the number of those cards the player controlled. Each player returns those cards to the battlefield under their control.