Gameplay Effect selector

Duration policy

Need	Duration policy	Notes
Damage, healing, purchase, permanent progression, initialization	Instant	Changes base value
Timed buff/debuff	Has Duration	Modifier exists while active
Equipped/aura/passive modifier removed by handle/condition	Infinite	Explicit removal required
Damage/heal over time	Has Duration or Infinite with Period	Period and duration/removal are separate decisions

Magnitude method

Need	Method
Constant or level-scaled data	Scalable Float / configured magnitude
Runtime caller supplies one named amount	SetByCaller on the Gameplay Effect Spec
Reusable magnitude from captured source/target attributes	Modifier Magnitude Calculation
Multi-stage authoritative result, multiple captures/outputs, custom damage resolution	Gameplay Effect Execution Calculation

Prefer the simplest method that expresses the rule. Calculations add implementation and prediction constraints; fixed/scalable modifiers remain easier to inspect.

Modifier operation

Choose the operation from the desired math—additive, multiplicative, division, or override— and test multiple simultaneous sources. Document whether percentages are intended to combine additively or multiplicatively; do not infer it from UI wording.

Runtime data

Gameplay Effect assets are immutable definitions. At runtime:

1. Make a Gameplay Effect Context with instigator/source information.
2. Make an outgoing Gameplay Effect Spec at the desired level.
3. Set SetByCaller magnitudes and other spec data before application.
4. Apply the spec to self or target ASC.
5. Retain the active effect handle when explicit removal or inspection is required.

Stacking design questions

• Aggregate by source or by target?
• Maximum stack count?
• Refresh, extend, or preserve duration on reapplication?
• Reset period on reapplication?
• Overflow behavior?
• Is each source independent, or should all instances combine?
• Which tags identify and inhibit the effect?

Test the exact configured behavior; stacking policy changes gameplay semantics, not just implementation.