By request I'm DMing an adventure with a lot of H.P. Lovecraft overtones, and the party has encountered the Big-Bad-Guy tentacle horror, a twenty foot Obyrith I've styled after the Far Realms Glothoma. It's nearly out of hit points, and I'd like it to cast one final spell without a TPK, but I'm worried I've chosen the wrong one due to the flavor text.
The description of the psychic scream spell (Xanathar's Guide to Everything, p. 163) states:
Each target must make an Intelligence saving throw. On a failed save,
a target takes 14d6 psychic damage and is stunned. On a successful
save, a target takes half as much damage and isn’t stunned. If a
target is killed by this damage, its head explodes, assuming it
has one.
Could someone parse this out for me? If a character takes enough damage to hit zero hitpoints, are they "dead" as far as this spell is concerned, suffering the homage to the movie Scanners, with the full head popping effect — or is dead only dead when they either fail enough death saving throws, or die instantly from the Massive Damage rule?
I ask because despite having two war clerics in their party, they're only level 6, which means the best they can respond with is revivify – which can't restore missing body parts:
You touch a creature that has died within the last minute. That
creature returns to life with 1 hit point. This spell can't return to
life a creature that has died of old age, nor can it restore any
missing body parts.
Best Answer
Killed by this damage isn't the same as reduced to 0
Monsters and PCs generally operate with slightly different rules regarding death. For most monsters, hitting 0 hit points means they die unless the DM intervenes to give them death saving throws. Players always operate per the the standard rules for Instant Death (PHB pg. 197):
Thus, players' heads only start exploding if they take enough damage to kill them outright. For the average PC Wizard at 6th level (assumes 14 Con) this would be about 35 damage past 0. On average, Psychic Scream does 49 damage or 24 if the save is successful.
Presumably the players are going to be smacked around a fair bit when this effect goes off, so this spell may well be in the realm of Save or Die for the more fragile characters. For the other characters, though, a successful save is still going to deal enough damage to potentially down them as well if it happens at the end of the fight.
Provided you're ok with players struggling on lots of death saves (totally reasonable with a Lovecraft theme, I think) then I think you'll be fine.