"It is all in my grasp. Every petty dream, every grand scheme, every soul, every fear. It all flows through me and from me."
—Memnarch

Fist of Suns

You may pay {W}{U}{B}{R}{G} rather than pay the mana cost for spells you cast.

"Willem put it on and started shooting sparks from his hands like some kind of wizard! Was supposed to be my turn next, but the blasted thing won't come off his hand. Send help."
—Brazen Coalition expedition dispatch

The Lost Caverns of Ixalan Commander

The List

Commander 2017

You may pay {W}{U}{B}{R}{G} rather than pay the mana cost for spells that you cast.

Fifth Dawn

You may pay {W}{U}{B}{R}{G} rather than pay the mana cost for spells that you play.

Fist of Suns's ability is an alternative cost to cast a spell. You can't combine this with other alternative costs, such as flashback. You can pay additional costs, such as kicker, in addition to this alternative cost.

If you apply Fist of Suns's alternative cost to a spell with {X} in its mana cost, X is 0.

If you cast a spell for which mana of any color can be spent to cast it, you may cast it for Fist of Suns's alternative cost and still spend any color of mana to cover that cost.

If you pay {W}{U}{B}{R}{G} rather than pay the mana cost of a spell with {X} in its mana cost, the only legal choice for X is 0.