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

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

Jack-in-the-Mox

{T}: Roll a six-sided die. This ability has the indicated effect.
1 — Sacrifice Jack-in-the-Mox and you lose 5 life.
2 — Add {W}.
3 — Add {U}.
4 — Add {B}.
5 — Add {R}.
6 — Add {G}.

Clifftop Retreat

Clifftop Retreat enters tapped unless you control a Mountain or a Plains.
{T}: Add {R} or {W}.

Contraband Livestock

Exile target creature, then roll a d20.
1—9 | Its controller creates a 4/4 green Ox creature token.
10—19 | Its controller creates a 2/2 green Boar creature token.
20 | Its controller creates a 0/1 white Goat creature token.

Clowning Around

Create two 1/1 white Clown Robot artifact creature tokens, then roll a six-sided die. If the result is equal to or less than the number of Robots you control, create a 1/1 white Clown Robot artifact creature token.

Strength-Testing Hammer

Whenever equipped creature attacks, roll a six-sided die. That creature gets +X/+0 until end of turn, where X is the result. Then if it has the greatest power or is tied for greatest power among creatures on the battlefield, draw a card.
Equip {3}

Barbarian Class

(Gain the next level as a sorcery to add its ability.)
If you would roll one or more dice, instead roll that many dice plus one and ignore the lowest roll.
{1}{R}: Level 2
Whenever you roll one or more dice, target creature you control gets +2/+0 and gains menace until end of turn.
{2}{R}: Level 3
Creatures you control have haste.

Mountain

Plains

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.

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

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

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

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.

Krark's Other Thumb

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