Conqueror's Flail

Equipped creature gets +1/+1 for each color among permanents you control.
As long as Conqueror's Flail is attached to a creature, your opponents can't cast spells during your turn.
Equip {2}

Jund Hackblade

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

Iridian Maelstrom

Destroy each creature that isn't all colors.

Naya Hushblade

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

Maze Abomination

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

Knight of New Alara

Each other multicolored creature you control gets +1/+1 for each of its colors.

Cloven Casting

Whenever you cast a multicolored instant or sorcery spell, you may pay {1}. If you do, copy that spell. You may choose new targets for the copy.

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.

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.

Brace for Impact

Prevent all damage that would be dealt to target multicolored creature this turn. For each 1 damage prevented this way, put a +1/+1 counter on that creature.

Springmantle Cleric

Springmantle Cleric enters with a +1/+1 counter on it for each color of mana spent to cast it.

Dragon Arch

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

Lobber Crew

Defender
{T}: Lobber Crew deals 1 damage to each opponent.
Whenever you cast a multicolored spell, untap Lobber Crew.

Niv-Mizzet Reborn

Flying
When Niv-Mizzet Reborn enters, reveal the top ten cards of your library. For each color pair, choose a card that's exactly those colors from among them. Put the chosen cards into your hand and the rest on the bottom of your library in a random order.

Mechtitan Core

{5}, Exile Mechtitan Core and four other artifact creatures and/or Vehicles you control: Create Mechtitan, a legendary 10/10 Construct artifact creature token with flying, vigilance, trample, lifelink, and haste that's all colors. When that token leaves the battlefield, return all cards exiled with Mechtitan Core except Mechtitan Core to the battlefield tapped under their owners' control.
Crew 2

Maze Sentinel

Vigilance
Multicolored creatures you control have vigilance.

Mana Cannons

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

Rogues' Gallery

For each color, return up to one target creature card of that color from your graveyard to your hand.

Tome of the Guildpact

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

Glinting Creeper

Converge — Glinting Creeper enters with two +1/+1 counters on it for each color of mana spent to cast it.
Glinting Creeper can't be blocked by creatures with power 2 or less.

General Ferrous Rokiric

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

All Suns' Dawn

For each color, return up to one target card of that color from your graveyard to your hand. Exile All Suns' Dawn.

Leyline of the Guildpact

If Leyline of the Guildpact is in your opening hand, you may begin the game with it on the battlefield.
Each nonland permanent you control is all colors.
Lands you control are every basic land type in addition to their other types.

Pillar of the Paruns

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

Chromatic Orrery

You may spend mana as though it were mana of any color.
{T}: Add {C}{C}{C}{C}{C}.
{5}, {T}: Draw a card for each color among permanents you control.

Pyroconvergence

Whenever you cast a multicolored spell, Pyroconvergence deals 2 damage to any target.

Niv-Mizzet, Guildpact

Flying, hexproof from multicolored
Whenever Niv-Mizzet, Guildpact deals combat damage to a player, it deals X damage to any target, target player draws X cards, and you gain X life, where X is the number of different color pairs among permanents you control that are exactly two colors.

Bant Sureblade

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

Hero of Precinct One

Whenever you cast a multicolored spell, create a 1/1 white Human creature token.

Faeburrow Elder

Vigilance
Faeburrow Elder gets +1/+1 for each color among permanents you control.
{T}: For each color among permanents you control, add one mana of that color.

Grixis Grimblade

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

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

Maze Rusher

Haste
Multicolored creatures you control have haste.

Skyrider Elf

Flying
Converge — Skyrider Elf enters with a +1/+1 counter on it for each color of mana spent to cast it.

Arcane Signet

{T}: Add one mana of any color in your commander's color identity.

Glass of the Guildpact

Multicolored creatures you control get +1/+1.

Maze Glider

Flying
Multicolored creatures you control have flying.

Awaken the Maelstrom

Awaken the Maelstrom is all colors.
Target player draws two cards. You may put an artifact card from your hand onto the battlefield. Create a token that's a copy of a permanent you control. Distribute three +1/+1 counters among one, two, or three creatures you control. Destroy target permanent an opponent controls.

Invasion of Alara

When Invasion of Alara enters, exile cards from the top of your library until you exile two nonland cards with mana value 4 or less. You may cast one of those two cards without paying its mana cost. Put one of them into your hand. Then put the other cards exiled this way on the bottom of your library in a random order.

Invasion of Alara // Awaken the Maelstrom

Gloryscale Viashino

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

Esper Stormblade

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

Bloom Tender

{T}: For each color among permanents you control, add one mana of that color.

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}.

O-Kagachi Made Manifest

O-Kagachi Made Manifest is all colors.
Flying, trample
Whenever O-Kagachi Made Manifest attacks, defending player chooses a nonland card in your graveyard. Return that card to your hand. O-Kagachi Made Manifest gets +X/+0 until end of turn, where X is the mana value of that card.

The Kami War

(As this Saga enters and after your draw step, add a lore counter.)
I — Exile target nonland permanent an opponent controls.
II — Return up to one other target nonland permanent to its owner's hand. Then each opponent discards a card.
III — Exile this Saga, then return it to the battlefield transformed under your control.