Effect

Use Effect when the target changes how strongly an existing Buff or Debuff applies to it. Multiply the creator's final Magnitude by the target's final Effect multiplier. Effect does not normally change application, duration, or the creator's Magnitude.

Effect is usually target-side

Effect modifiers usually belong to the player or monster affected by the Buff or Debuff. Wording such as reduced effect of Shock on you changes the Shock after it reaches that target.

Magnitude and Effect multiply

The creator first determines the effect's Magnitude. The target's Effect multiplier then scales that value. Creator-side increased Magnitude and target-side reduced Effect do not cancel inside one increased modifier total.

Specific wording limits the scope

Reduced effect of Shock on you applies to Shock. Reduced effect of Curses on you applies to Curses. Increased effect of Arcane Surge on you applies to Arcane Surge. None of those wordings is a universal modifier to every Buff or Debuff.

Duration is separate

Effect does not normally make a Buff or Debuff last longer or expire faster. Shock Effect and Shock duration, for example, are separate modifier scopes and can appear as separate properties on the same Rune.

Application is separate

Reduced Effect does not by itself prevent the Buff or Debuff from being applied. Unaffected is a separate state: the Debuff can remain on the target but does not apply its effect.

Effect is not Magnitude

A 0.5.0 correction changed Low Tolerance's description from increased Effect of Poison to increased Magnitude. This distinction matters because Poison Magnitude belongs to the creator, while Effect belongs to the affected target.

Same-type stacking rules still apply

Effect changes the strength of the active Buff or Debuff. It does not override the normal rule that same-type Buffs and Debuffs use only the strongest copy unless the mechanic explicitly stacks.