So, the spell hits 5 creatures and they all fail the Str check. Do you roll 2d6 for each creature that the arms hit or just roll once for the damage that affects each of the 5?
[RPG] How does damage from Arms of Hadar get assigned
dnd-5espellswarlock
Best Answer
It's one damage roll, it's applied to all characters.
How I do this in my games is have the damage rolled before anyone makes their save. So the caster determines the damage before the saves are rolled.
Then each character makes their save and the effects are adjudicated after the saving throws are made.
Page 196 of the PHB has this rule: