During the planning process of a new character I came across the following question.
What is the damage when you get a critical hit with acid arrow?
Lets take a look at acid arrow cast at CL3, and lets assume we confirm the critical hit. This means we have the initial damage, plus one round.
I haven't found anywhere which disagrees with the damage from the initial hit benefiting from the critical multiplier. Its an attack spell that requires an attack roll after all, and is not precision damage.
What seems to be in question is the damage of the following round. Is it 2d4 or 4d4 each following round?
If we look at other spells that require an attack roll, lets take shocking grasp cast at CL3. On a regular hit it deals 3d6, but when you crit it deals 6d6. At its highest it would be 5d6 to 10d6.
So why would a lower level spell be allowed to out damage a higher level spell? Yes the higher level spell can eventually deal more damage, but that can also be negated, and takes longer to build up.
The critical hit rules are fairly silent about this as they simply state spells can crit and that damage is doubled. Thats fine for instantaneous spells like shocking grasp, but it leaves out duration spells.
A spell that requires an attack roll can score a critical hit. A spell attack that requires no attack roll cannot score a critical hit. If a spell causes ability damage or drain (see Special Abilities), the damage or drain is doubled on a critical hit.
This question is much the same but is for D&D 5e.
There was a forum about this topic but it doesn't answer the question well.