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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.

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  • \$\begingroup\$ Has your DM previously run or played D&D 4th edition? \$\endgroup\$ – V2Blast Dec 15 '19 at 2:31
  • \$\begingroup\$ I think he has, yeah. Not something I’ve ever tried, though. \$\endgroup\$ – royalmurder Dec 15 '19 at 2:32
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This is a houserule

The section on Critical Hits states:

When you score a critical hit, you get to roll extra dice for the attack's damage against the target. Roll all of the attack's damage dice twice and add them together. Then add any relevant modifiers as normal. To speed up play, you can roll all the damage dice at once [...]

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):

All magic weapons and implements give you an enhancement bonus to your attack rolls and damage rolls when you use them to make an attack [...]

All magic weapons and implements deal one or more extra dice of damage on a critical hit. The number of extra dice is equal to the item’s enhancement bonus [...]

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    \$\begingroup\$ I checked on a hunch, and something very close to this particular mechanic is actually part of 4e's rules: "All magic weapons and implements deal one or more extra dice of damage on a critical hit. The number of extra dice is equal to the item’s enhancement bonus [...]" It is possible that the DM has previously run 4e and is carrying edition baggage. \$\endgroup\$ – Carcer Dec 15 '19 at 2:16
  • \$\begingroup\$ @Carcer Oh that's a great point, I'd forgotten about that rule \$\endgroup\$ – Medix2 Dec 15 '19 at 2:19
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    \$\begingroup\$ Perhaps worth mentioning that 5e does have a mechanic of bonus dice on crit, but instead of being from magic weapons it's an Orc racial (Savage Attacks: +1 die) and a Barbarian class feature (Brutal Critical: +1 to +3 with level) for a max of 6d12 with a greataxe crit for an Orc barbarian. \$\endgroup\$ – Peter Cordes Dec 15 '19 at 13:55
  • \$\begingroup\$ Whether this makes the weapon actually stronger depends entirely on whether the damage replaces the normal damage bonus on all hits or is a bonus on top of that. In the former case assuming you've got a d12 weapon and a 50% chance to hit, no (dis)advantage, the expected damage increase of the magical weapon (ignoring the increased chance to hit) would be \$\frac{n \cdot 13}{40}\$ with the house rule vs the \$\frac{20 \cdot n}{40}\$ increase for the static bonus... \$\endgroup\$ – fabian Dec 15 '19 at 17:58
  • \$\begingroup\$ @fabian I see what you mean, but there's no reason to assume that the usual +x bonus to attack/damage rolls has gone away. Given that the OP didn't ask or mention anything about that and the +x bonus was already a thing in 4e it would be especially odd if the static +x bonus were removed. Earlier comments removed since I now understand what you meant. \$\endgroup\$ – Medix2 Dec 15 '19 at 18:13

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