FOILCheapest priced copy (March of the Machine): $0.49 at Card Kingdom, near mint, their price list as of .
Omnath, Locus of All 
Legendary Creature — Phyrexian Elemental · 4/4 · Rare · March of the Machine Promos · #249s
If you would lose unspent mana, that mana becomes black instead.
At the beginning of your first 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.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
5 printings · $0.49 to $1.29 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| March of the Machine | 249 | Rare | $0.49 | $0.79 |
| March of the Machine | 313 | Rare | $0.49 | $0.49 |
| March of the Machine | 387 | Rare | — | $0.69 |
| March of the Machine Promos | 249p | Rare | $0.49 | $0.49 |
| March of the Machine Promos | 249s | Rare | — | $1.29 |
4 rulings from Wizards of the Coast
- 14 April 2023As long as Omnath, Locus of All remains under your control, you'll retain unspent mana as steps and phases end, although that mana will become black. This means you can add mana and spend it during a future step, phase, or turn. Once Omnath leaves your control, you'll have until the end of the current step or phase to spend the mana before it is lost.
- 14 April 2023The mana symbols in the card you reveal may be in any combination of colors. For example, you could reveal a card with mana cost {1}{R}{R}{R}, one with mana cost {4}{U}{R}{W}, one with mana cost {W}{U}{B}{R}{G}, or one with mana cost {R/G}{G}{G/W}.
- 14 April 2023If unspent mana you have has any restrictions or riders associated with it (for example, if it was produced by Omen Hawker), those restrictions or riders remain associated with that mana when it becomes black.
- 14 April 2023Omnath's last ability isn't a mana ability even though it can cause you to add mana. It uses the stack and can be responded to.