School of Arithmophobia

The School of Arithmophobia is a strange arcane tradition built around the idea that numbers themselves can be weaponized. Its wizards turn combat into a test of mental speed, forcing the Dungeon Master to solve rapid-fire arithmetic problems while spells are already flying and enemies are moving.

Practitioners of this school learn to bind magical effects to simple operations such as addition, subtraction, multiplication, and division. A correct answer may allow reality to proceed normally, but a mistake can cause a spell to spread to additional targets, weaken every enemy on the battlefield, multiply magical damage, or temporarily erase creatures from combat entirely.

As an Arithmophobia wizard grows in power, the problems become more complex and the consequences more severe. Equations can cause enemies to turn on one another, correct answers can be challenged with immediate recalculation, and the most powerful practitioners can invoke the impossible concept of dividing by zero to catastrophically disrupt reality itself.

To study the School of Arithmophobia is to understand one simple truth: in battle, the most dangerous number is the one your enemy cannot solve fast enough.

Level 3: Math Challenge

Once per turn, when you cast a Wizard spell or cantrip, you can issue one Math Challenge to the DM.

The player creates the problem.

Rules:

• Numbers used can range from 1 to 1,000
• No calculators
• Timer starts only after the full problem has been spoken
• Wrong answer or no answer before time expires triggers the chosen effect
• Division and Equation problems must resolve to whole-number answers

Addition — 3 seconds
If answered incorrectly, roll 1d6. Choose that many additional creatures to be affected by the triggering spell.

This works with:

• single-target spells
• multi-target spells
• AoE spells

For AoEs, the extra creatures can be outside the normal area, as long as they’re within the spell’s range.

Subtraction — 3 seconds
If answered incorrectly, roll 1d4. Until the start of your next turn, every enemy creature in combat subtracts that number from every attack roll it makes.

Multiplication — 5 seconds
If answered incorrectly, roll 1d6. Multiply the triggering spell’s damage by that number.

The multiplication happens before resistances or other damage reduction.

No cap.

Division — 5 seconds
If answered incorrectly, roll 1d6. Choose up to that many enemy creatures you can see. Those creatures are erased from combat until the start of your next turn.

While erased, they:

• can’t act
• can’t move
• can’t be targeted
• can’t take damage
• can’t affect the battlefield

They return at the start of your next turn to their previous spaces, or the nearest unoccupied spaces.

Level 6: Equation

You can now issue an Equation Math Challenge.

An Equation can contain:

• no more than 3 numbers
• no more than 2 operations
• numbers from 1–1,000
• a whole-number result

The DM has 8 seconds.

If answered incorrectly or too late, until the start of your next turn, every enemy creature can target only other enemy creatures with attacks and harmful abilities.

If an enemy has no valid enemy target, it can’t make an attack or use a harmful ability that turn.

Level 10: Recalculate

When the DM answers one of your Math Challenges correctly, you can force them to answer a second, different problem of the same type.

The second problem:

• must be different from the first
• uses the same operation or challenge type
• gets a fresh full timer
• triggers the normal effect if answered incorrectly or too late

You can use Recalculate a number of times equal to your Intelligence modifier per Long Rest.

Level 14: Divide By Zero

Once per Long Rest, choose any number of enemy creatures you can see.

Each creature makes an Intelligence saving throw against your Wizard spell save DC.

On a failed save:

• the creature is immediately reduced to 0 Hit Points

On a successful save:

• the creature takes 10d10 Force damage

No Math Challenge is required for Divide by Zero.