Cheapest priced copy (Commander 2017): $0.49 at Card Kingdom, near mint, their price list as of .
Magus of the Mind 
Creature — Human Wizard · 4/5 · Rare · Commander 2017 · #12
{U}, {T}, Sacrifice this creature: Shuffle your library, then exile the top X cards, where X is one plus the number of spells cast this turn. Until end of turn, you may play lands and cast spells from among cards exiled this way without paying their mana costs.
Legal inCommanderLegacyVintage
Not legal inBrawlStandardPioneerModernPauper
1 printing · $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Commander 2017 | 12 | Rare | $0.49 | — |
6 rulings from Wizards of the Coast
- 25 August 2017If you cast a card “without paying its mana cost,” you can’t pay any alternative costs. You can, however, pay additional costs. If the card has any mandatory additional costs, such as that of Tormenting Voice, those must be paid to cast the card.
- 25 August 2017Any of the cards you don’t play will remain in exile.
- 25 August 2017If 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.
- 25 August 2017You must follow the normal timing permissions and restrictions for cards you cast this way.
- 25 August 2017If no spells have been cast in the turn you activate Magus of the Mind’s ability, X is one.
- 25 August 2017You may play a land exiled this way only if you have an available land play this turn.