Pyroconvergence

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

General Ferrous Rokiric

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

Widespread Thieving

Hideaway 5 (When this enchantment enters the battlefield, look at the top five cards of your library, exile one face down, then put the rest on the bottom in a random order.)
Whenever you cast a multicolored spell, create a Treasure token. Then you may pay {W}{U}{B}{R}{G}. If you do, you may play the exiled card without paying its mana cost.

Omnath, Locus of All

If you would lose unspent mana, that mana becomes black instead.
At the beginning of your precombat main phase, look at the top card of your library. You may reveal that card if it has three or more colored mana symbols in its mana cost. If you do, add three mana in any combination of its colors and put it into your hand. If you don't reveal it, put it into your hand.

Esper Stormblade

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

Knight of New Alara

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

Glass of the Guildpact

Multicolored creatures you control get +1/+1.

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.)

Jund Hackblade

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

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.)

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.

Tome of the Guildpact

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

Obsidian Obelisk

Obsidian Obelisk enters the battlefield tapped.
{T}: Add {C}.
{T}: Add one mana of any color. Spend this mana only to cast a multicolored spell.

Madrush Cyclops

Reborn Hope

Return target multicolored card from your graveyard to your hand.

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.

Bant Sureblade

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