Cheapest priced copy (Mystery Booster 2): $9.99 at Card Kingdom, near mint, their price list as of .
Mental Misstep 
Instant · Uncommon · The Zeta Set · #264
({U/P} can be paid with either {U} or 2 life.)
Counter target spell with mana value 1.
Legal inCommander
Restricted inVintage
Banned inModernLegacy
Not legal inBrawlStandardPioneerPauper
9 printings · $9.99 to $399.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Mystery Booster 2 | 30 | Uncommon | $9.99 | — |
| New Phyrexia | 38 | Uncommon | $11.99 | $229.99 |
| Eternal Weekend | 2023a | Rare | — | — |
| Media and Collaboration Promos | 2023-1 | Rare | — | $399.99 |
| Secret Lair Drop | 1179 | Rare | $94.99 | $179.99 |
| Secret Lair Drop | 2373 | Rare | $20.99 | $21.99 |
| The Zeta Set | 22 | Uncommon | — | — |
| The Zeta Set | 143 | Uncommon | — | — |
| The Zeta Set | 264 | Uncommon | — | — |
7 rulings from Wizards of the Coast
- 1 June 2011Each Phyrexian mana symbol in a spell's mana cost contributes 1 to that spell's mana value. For example, Mental Misstep's mana value is 1, regardless of how its cost was paid.
- 1 June 2011To calculate the mana value of a card with Phyrexian mana symbols in its cost, count each Phyrexian mana symbol as 1.
- 1 June 2011If a spell has {X} in its mana cost, X is considered to be the value chosen for it while that spell is on the stack.
- 1 June 2011As you cast a spell or activate an activated ability with one or more Phyrexian mana symbols in its cost, you choose how to pay for each Phyrexian mana symbol at the same time you would choose modes or choose a value for X.
- 1 June 2011A card with Phyrexian mana symbols in its mana cost is each color that appears in that mana cost, regardless of how that cost may have been paid.
- 1 June 2011If you're at 1 life or less, you can't pay 2 life.
- 1 June 2011Phyrexian mana is not a new color. Players can't produce Phyrexian mana.