Goblin Cruciverbalist

Haste
When Goblin Cruciverbalist enters, create a colorless artifact token named your choice of A, E, I, O, or U.
Whenever Goblin Cruciverbalist attacks, using the first letters of the names of permanents you control, spell a word you haven't spelled this game. It gets +1/+0 until end of turn for each letter in that word.

Surprise Party

When Surprise Party enters, yell "Surprise!" and put onto the battlefield any number of printed Clown Robot tokens that aren't touching each other, that you hid on the battlefield before you cast Surprise Party, and that weren't spotted by an opponent before you cast Surprise Party.
Robots you control get +1/+0 and have vigilance.

Non-Human Cannonball

When Non-Human Cannonball dies, roll a six-sided die. If the result is 4 or less, Non-Human Cannonball deals that much damage to you.

Nearby Planet

Rangeling (This card is every land type, including Plains, Island, Swamp, Mountain, Forest, Desert, Gate, Lair, Locus, and all those Urza's ones.)
Nearby Planet enters tapped.
When Nearby Planet enters, sacrifice it unless you pay {1}.

Ticking Mime Bomb

When Ticking Mime Bomb enters, without speaking or indicating any specific creature, pantomime to a person outside the game, then they choose a creature you don't control. Ticking Mime Bomb deals damage equal to twice the number of Robots you control to the chosen creature.

Pietra, Crafter of Clowns

Haste
Robots you control get +1/+1.
{R}{W}, {T}, Tell a joke you haven't told this game to someone outside the game: Create a 1/1 white Clown Robot artifact creature token. If that person laughed, the token gains haste until end of turn.

Starlight Spectacular

Parade! — At the beginning of combat on your turn, choose creatures you control one at a time until each creature you control has been chosen. Each of those creatures gets +1/+1 until end of turn for each creature chosen before it. (Places everyone! The first creature in line gets +0/+0.)

Circuits Act

Roll three six-sided dice. For each different result, create a 1/1 white Clown Robot artifact creature token.

Mountain

Devil K. Nevil

Haste
When Devil K. Nevil enters, jump it over any number of creatures. If it clears those creatures, put that many +1/+1 counters on it. (You can see a jumping demonstration at DevilKNevil.com.)

Pie-roclasm

Pie-roclasm deals π damage to each non-Clown creature. (How to calculate π isn't important. It's a smidgen more than 3.)

Omniclown Colossus

Affinity for Clowns (This spell costs {1} less to cast for each Clown you control.)
Trample

Omniclown Colossus // Pie-roclasm

One-Clown Band

{2}{R}: Target Robot gets +2/+0 until end of turn.

Juggletron

Trample
Whenever Juggletron attacks, you may put an art sticker on it.
Juggletron gets +3/+0 for each item in its art that's not touching Juggletron, another item, or the card frame.

Impounding Lot-Bot

When Impounding Lot-Bot enters, you may say "INCARCERATE!" in a robot voice. If you do, exile another target artifact or enchantment until Impounding Lot-Bot leaves the battlefield.

T.A.P.P.E.R.

{T}, Tap an untapped creature you control that has a hat: Tap target creature.

Plains

Clown Car

When Clown Car enters, roll X six-sided dice. For each odd result, create a 1/1 white Clown Robot artifact creature token. For each even result, put a +1/+1 counter on Clown Car.
Crew 2

Celebr-8000

At the beginning of combat on your turn, roll two six-sided dice. For each result of 1, Celebr-8000 gets +1/+1 until end of turn. For each other result, it gains the indicated ability until end of turn. If you rolled doubles, it also gains double strike until end of turn.
• 2 — menace
• 3 — vigilance
• 4 — lifelink
• 5 — flying
• 6 — indestructible

Assembled Ensemble

Vigilance
Assembled Ensemble's power is equal to the number of Robots you control.
Whenever you cast a spell with an artifact creature in its art, create a 1/1 white Clown Robot artifact creature token.