My DM runs his game without allowing players access to homebrew options – including Unearthed Arcana – but something came up last season that gave me pause for thought.
A player’s character – a 4th level Way of the Sun Soul Monk – critically hit an enemy with a +1 hand-axe.
I was expecting the damage dice to be rolled at 2d6 plus some static damage as the enemy has no discernible weaknesses, but the DM called for 3d6.
I curiously asked him why it was 3, and he said:
A magic weapon with a + bonus adds that many of the weapons damage die to critical hits.
My question is; is this a house rule? It hasn’t come up before (somehow) and I can’t find any mention of this in the rulebooks I have access to.
Best Answer
This is a houserule
The section on Critical Hits states:
Note that you only roll the attack's damage dice twice, nothing else is doubled, such as modifiers, and no additional dice specifically occur when using a magic item. This is also explained in the following two questions:
Also, no part of the section on Magic Items states that they have this special property on a critical hit. Your GM saying that a +n longsword rolls (2+n)d6 is a houserule, and a rather strong one at that as it makes magic items even more powerful than they already are.
It also is rather strange because it means a 1d4 weapon will not benefit as much as a 1d12 weapon; normally one weapon could roll 2d4 on a crit and another 2d12, but with this houserule one could roll 5d4 and another 5d12. These are much farther apart in terms of their expected damage. Going from a difference of 8, to a difference of 20.
Your GM may be applying a rule that did exist in 4th-edition (thanks to Carcer for pointing this out):