Simultaneous Effect

When two or more effects happen at the same instant, they are simultaneous. The rules resolve them in this order:

1. Turn order takes priority. If the simultaneous effects are tied to creatures' turns, resolve them in initiative order; the creature whose turn it is acts first.
2. The creature triggering the effect chooses the order. If one creature's action causes multiple simultaneous effects (a spell that both damages and applies a condition), that creature decides which resolves first.
3. Player Characters before NPCs (DM's option). Some tables prefer to resolve PC effects before NPC effects when truly tied; the SRD allows the DM to adopt this as a house rule.
4. DM call when none of the above resolves it. If the order genuinely cannot be determined by rules, the DM decides — favoring the resolution that produces the clearest, fairest outcome.

Common situations:

• A creature drops to 0 HP and triggers a death-throes effect that damages the killer: resolve the killer's hit first (which dropped the creature), then the death effect
• Two creatures hit each other on the same turn with simultaneous reactions (rare): each resolves their effect against the other's pre-effect state
• A creature steps on a trap that triggers as a reaction: the step completes, then the trap fires; if the trap is interruption-style (a magic mouth shouts), it interrupts mid-step
• Two damage-over-time effects tick at the start of the same turn: the affected creature's owner (player or DM) chooses the order

Why this rule exists: D&D's action economy is sequential, but the fiction often produces apparent simultaneity. The rule keeps resolution unambiguous and forward-moving rather than recursing into infinite priority debates.