Epic Experiment

Exile the top X cards of your library. You may cast instant and sorcery spells with mana value X or less from among them without paying their mana costs. Then put all cards exiled this way that weren't cast into your graveyard.

Pioneer Masters

Outlaws of Thunder Junction Commander

Commander 2021

Time Spiral Remastered

Exile the top X cards of your library. You may cast instant and sorcery spells with converted mana cost X or less from among them without paying their mana costs. Then put all cards exiled this way that weren't cast into your graveyard.

Commander 2015

Exile the top X cards of your library. For each instant and sorcery card with converted mana cost X or less among them, you may cast that card without paying its mana cost. Then put all cards exiled this way that weren't cast into your graveyard.

If the card has {X} in its mana cost, you must choose 0 as the value of X when casting it without paying its mana cost.

If you can't cast a card, perhaps because there are no legal targets available, or if you choose not to cast it, it will be put into your graveyard.

If you cast a card "without paying its mana cost," you can't choose to cast it for any alternative costs. You can, however, pay additional costs. If the card has any mandatory additional costs, you must pay those to cast the card.

When casting an instant or sorcery card this way, ignore timing restrictions based on the card's type. Other timing restrictions, such as "Cast [this card] only during combat," must be followed.

You cast the cards one at a time, choosing modes, targets, and so on. The last card you cast will be the first one to resolve.