rather than pay the mana cost for a colorless spell you cast from your hand.Darksteel Monolith can make one colorless spell from your hand cost zero each turn. That offers a dramatic payoff for decks filled with expensive Eldrazi, artifacts, and other colorless spells. Once the eight-mana artifact is established, a single substantial follow-up can recover much of the investment immediately.
The spell is still cast, so Eldrazi cast triggers remain available. That distinguishes the Monolith from effects that simply put a creature onto the battlefield. It can therefore support threats whose value comes from both casting and entering. Colorless instants or spells with flash can also use the permission on opponents' turns, since the limit is once each turn rather than once each round.
Only spells cast from your hand qualify. A commander in the command zone or a card being cast from the graveyard does not receive this alternative cost through the Monolith. Additional costs still apply, and an X in the mana cost normally must be chosen as zero when using the free alternative cost.
Indestructible helps the artifact survive destruction, but exile and bounce remain relevant. Have useful cards in hand before committing eight mana; an empty-handed Monolith does not generate its own threats. The strongest home is a deck that already ramps heavily and draws enough cards to keep presenting expensive colorless plays. It turns those cards into a much faster sequence while preserving the benefits of actually casting them.
