An X in a mana cost turns one spell into a flexible tool, but it also raises several questions: when is X chosen, how do reductions work and what is the spell's mana value?
Keep three ideas separate: the chosen value of X, the total cost paid and the mana value. This guide complements our article on the mana curve and our guide to the stack and priority.
Step 1: choose X while casting
When casting a spell whose cost contains X, choose X during the casting process. If the printed cost is XRR and X is 3, the base cost contains three generic mana and two red mana. Announce “X equals 3” before payment so the choice is clear and fixed for that spell on the stack.
Step 2: calculate the total cost
The printed symbols are not always the final amount. An alternative cost may apply, additional costs or increases may be added, and reductions may then lower what must be paid.
For XRR with X = 4, the base is 4RR. A reduction of one generic mana can make the payment 3RR, but X remains 4. The spell’s effect still uses 4.
- Announce the spell and modes.
- Choose X.
- Identify the base or alternative cost.
- Add additional costs and increases.
- Apply reductions.
- Check coloured requirements and pay.
Mana value: X counts on the stack
Mana value comes from the mana cost, not from the amount actually paid. On the stack, the chosen value of X is included. XRR with X = 4 therefore has mana value 6, even if a reduction lowered the payment.
In the library, hand, graveyard or exile, X is generally 0 when calculating mana value. The same XRR card has mana value 2 there. See our guide to Magic zones to locate the card first.
| Situation | X used | XRR example |
|---|---|---|
| On stack, X = 4 | 4 | Mana value 6 |
| In hand | 0 | Mana value 2 |
| In graveyard | 0 | Mana value 2 |
| Cost reduced by one | 4 | Lower payment, mana value 6 |
Casting without paying the mana cost
If an effect lets you cast a card without paying its mana cost and nothing else defines X, the legal choice is generally X = 0. Free casting does not grant an arbitrarily large X. Mandatory additional costs may still have to be paid.
Payment is not mana value
A reduction changes what you pay, not the printed mana cost. An additional cost may increase payment without increasing mana value. For XRR with X = 4, you might pay 3RR after a reduction while the spell still has mana value 6 and uses X = 4.
Choose X with a plan
The largest possible X is not always best. Keeping mana open may protect the spell, activate an ability or cast another card. Choose the smallest X that achieves the needed result, then compare it with the value of keeping resources available.
Final checklist
- Is X clearly announced?
- Did I identify the base or alternative cost?
- Were additions, increases and reductions applied?
- Does payment meet coloured requirements?
- Is mana value calculated for the current zone?
Explore Magic: The Gathering products and practise announcing X before calculating each cost.