Card Spotlight
A 3-mana colorless rock that taps for three and untaps itself for three. That nets zero on its own, and infinite mana once anything makes untapping it cheaper or free.
Commander Spotlight
Basalt Monolith ↗
A 3-mana colorless rock that taps for three and untaps itself for three. That nets zero on its own, and infinite mana once anything makes untapping it cheaper or free.
See Basalt Monolith's full stats and printings →
Not a commander. It's an artifact with no legendary creature version, so it only ever shows up as a mana rock or combo piece in someone else's deck.
A staple-tier mana rock in colorless-friendly decks and a combo enabler in artifact or high-power shells running Rings of Brighthearth or Power Artifact, without being a dead card in a list that never draws either.
Rings of Brighthearth ↗
Copies the untap ability for {2}, netting one colorless mana per loop, which repeats for infinite mana.
Power Artifact ↗
Reduces the untap cost to {1}, making Basalt Monolith an infinite colorless mana source with no third card.
Sol Ring ↗
Another cheap rock that helps get to the mana needed to activate Basalt Monolith more than once a turn.
Metalworker ↗
A creature that adds {C}{C} for each artifact card you reveal from your hand, another colorless mana burst for the same artifact-heavy deck.
Basalt Monolith is inexpensive and worth owning as a mana rock alone, before any combo consideration. Power Artifact carries most of that line's price and rarity, so the combo itself is the more expensive half of the equation.
Rings of Brighthearth copies its untap ability for {2}, so {5} buys two untaps and six mana, a net gain of one mana per loop. You can repeat the loop as often as you like, so the pair makes infinite colorless mana once you have {2} extra to start. Power Artifact is the other two-card combo: it reduces the untap cost to {1}, so each loop nets two mana with no other card needed.
Yes. Even ignoring both combo lines, it's a fine three-mana rock that makes {C}{C}{C} at once for a big spell. It doesn't untap on its own, and paying {3} to untap it nets no mana, so most decks untap it at the end of an opponent's turn with mana they would not otherwise use.
Power Artifact is a narrow, otherwise-unplayable enchantment outside this exact combo, so decks running it are almost always building specifically around this line rather than finding it incidentally. That keeps it rarer at the table than Sol Ring or Isochron Scepter combos.