Jenson Carthalion, Druid Exile

Whenever you cast a multicolored spell, scry 1. If that spell was all colors, create a 4/4 white Angel creature token with flying and vigilance.
{5}, {T}: Add {W}{U}{B}{R}{G}.

Maze Abomination

Deathtouch (Any amount of damage this deals to a creature is enough to destroy it.)
Multicolored creatures you control have deathtouch.

Infinite Guideline Station

When Infinite Guideline Station enters, create a tapped 2/2 colorless Robot artifact creature token for each multicolored permanent you control.
Station (Tap another creature you control: Put charge counters equal to its power on this Spacecraft. Station only as a sorcery. It's an artifact creature at 12+.)
12+ | Flying
Whenever Infinite Guideline Station attacks, draw a card for each multicolored permanent you control.

Maze Sentinel

Vigilance
Multicolored creatures you control have vigilance.

Guildmages' Forum

{T}: Add {C}.
{1}, {T}: Add one mana of any color. If that mana is spent on a multicolored creature spell, that creature enters with an additional +1/+1 counter on it.

General Ferrous Rokiric

Hexproof from monocolored
Whenever you cast a multicolored spell, create a 4/4 red and white Golem artifact creature token.

Scuttling Butler

At the beginning of combat on your turn, if you control two or more multicolored permanents, this creature gains double strike until end of turn.

Maze Behemoth

Trample
Multicolored creatures you control have trample.

Jund Hackblade

As long as you control another multicolored permanent, this creature gets +1/+1 and has haste.

Urza's Filter

Multicolored spells cost {2} less to cast.

Tome of the Guildpact

Whenever you cast a multicolored spell, draw a card.
{T}: Add one mana of any color.

Gloryscale Viashino

Whenever you cast a multicolored spell, this creature gets +3/+3 until end of turn.

Demand

Search your library for a multicolored card, reveal it, put it into your hand, then shuffle.

Supply

Create X 1/1 green Saproling creature tokens.

Supply // Demand

Mana Cannons

Whenever you cast a multicolored spell, this enchantment deals X damage to any target, where X is the number of colors that spell is.

Obsidian Obelisk

This artifact enters tapped.
{T}: Add {C}.
{T}: Add one mana of any color. Spend this mana only to cast a multicolored spell.

Pillar of the Paruns

{T}: Add one mana of any color. Spend this mana only to cast a multicolored spell.

Rampaging Monument

Trample
This creature enters with three +1/+1 counters on it.
Whenever you cast a multicolored spell, put a +1/+1 counter on this creature.

Glittering Wish

You may reveal a multicolored card you own from outside the game and put it into your hand. Exile Glittering Wish.

Countersquall

Counter target noncreature spell. Its controller loses 2 life.

Jared Carthalion

+1: Create a 3/3 Kavu creature token with trample that's all colors.
−3: Choose up to two target creatures. For each of them, put a number of +1/+1 counters on it equal to the number of colors it is.
−6: Return target multicolored card from your graveyard to your hand. If that card was all colors, draw a card and create two Treasure tokens.
Jared Carthalion can be your commander.

Grixis Grimblade

As long as you control another multicolored permanent, this creature gets +1/+1 and has deathtouch. (Any amount of damage it deals to a creature is enough to destroy that creature.)

Psychotic Fury

Target multicolored creature gains double strike until end of turn.
Draw a card.

Dragon Arch

{2}, {T}: You may put a multicolored creature card from your hand onto the battlefield.

Obscura Charm

Choose one —
• Return target multicolored permanent card with mana value 3 or less from your graveyard to the battlefield tapped.
• Counter target instant or sorcery spell.
• Destroy target creature or planeswalker with mana value 3 or less.

Dimir Charm

Choose one —
• Counter target sorcery spell.
• Destroy target creature with power 2 or less.
• Look at the top three cards of target player's library. Put one back and the rest into that player's graveyard.

Maze Rusher

Haste
Multicolored creatures you control have haste.

Rienne, Angel of Rebirth

Flying
Other multicolored creatures you control get +1/+0.
Whenever another multicolored creature you control dies, return it to its owner's hand at the beginning of the next end step.

Vivid Revival

Return up to three target multicolored cards from your graveyard to your hand. Exile Vivid Revival.

Glass of the Guildpact

Multicolored creatures you control get +1/+1.

Naya Hushblade

As long as you control another multicolored permanent, this creature gets +1/+1 and has shroud. (It can't be the target of spells or abilities.)

Drown in the Loch

Choose one —
• Counter target spell with mana value less than or equal to the number of cards in its controller's graveyard.
• Destroy target creature with mana value less than or equal to the number of cards in its controller's graveyard.

Bant Sureblade

As long as you control another multicolored permanent, this creature gets +1/+1 and has first strike.

Esper Stormblade

As long as you control another multicolored permanent, this creature gets +1/+1 and has flying.