Adamantine armour/weapons made by the drow are said to degrade if exposed to sunlight, but does this apply to gear crafted from adamantine by other races as well?
[RPG] Does all adamantine gear deteriorate in sunlight
dnd-5eequipmentspecial-materials
Related Solutions
Find one as treasure / Go on a quest for it
By the book is a little odd to ask for here — the place to find an adamantine weapon is in the game world, not in some rule in the PHB that would give players unfettered access to powerful treasure.
For a veneer of by-the-book analysis, unenchanted adamantine items are listed as magic items in the DMG (pp. 146–8, 150). There's only armour listed, but adding an adamantine weapon to a treasure trove would be a trivial bit of homebrewing (that many DMs wouldn't even consider homebrewing).
So the answer is: go on a quest for adamantine, either in weapon form, or raw material form and then a second quest to find the legendary smith who can work “one of the hardest substances in existence.” Or mention the desire to your DM, and get lucky finding it in a treasure cache. That's how you get an adamantine weapon.
Yes, the natural 20 is still an automatic hit
We know that a critical hit is, by definition, an automatic hit regardless of AC thanks to the basic rules for making an attack:
If the d20 roll for an attack is a 20, the attack hits regardless of any modifiers or the target's AC. This is called a critical hit, which is explained later in this section.
If you score a critical hit, you must have hit.
The armor states (emphasis mine):
While you're wearing it, any critical hit against you becomes a normal hit.
By saying "a normal hit" instead of "a normal attack roll" (or something similar) the armor explicitly does not change the result of the attack roll (hit or miss), but rather the severity of the hit (critical or normal).
That suggests the following sequence of events:
- Attack roll is made against you
- The roll is a natural 20, which means it's an automatic hit and also a critical hit
- The effect of the armor kicks in, the critical hit becomes a regular hit.
By the time the item interferes, we've already established the attack as a hit and the armor doesn't undo that hit; it reduces the severity of the hit.
But What about for Champion Fighters?
Champion Fighters have class features which give them an expanded critical hit range
Beginning when you choose this archetype at 3rd level, your weapon attacks score a critical hit on a roll of 19 or 20.
Starting at 15th level, your weapon attacks score a critical hit on a roll of 18–20.
It's already been established in a related question that these improved criticals are also automatic hits
Improved Critical specifically says you score a critical hit on a 19 or 20. A critical hit is a type of hit; by scoring one, you've also scored a hit. If the word 'critical' wasn't there, the ability would certainly read as if you couldn't miss on a 19 or 20.
So, the attack is a critical hit, which means that the adamantine armor makes it a normal hit. So, if you face any creatures with improved critical hit ranges, they will still automatically hit you on a natural roll that falls within their range. However, those automatic hits become regular hits just like a critical hit from a natural 20.
We're almost certain this is Rules-As-Intended
Jeremy Crawford, lead rules designer for 5e, has stated over twitter:
Does the nat 20 still auto hit against adamantine armor?
Yes.
While no longer an official source, Jeremy's tweets still provide an excellent look into the intent of the design. Especially since he made this particular tweet back when his rulings were official. Based on this, we can be confident that this stance is the intended reading of the rules.
Best Answer
No, sunlight-sensitive gear is a Drow-specific thing, not a general property of adamantine
(OOC -- what do Drow make their gear from? PVC with no UV-resistance modifiers? :P)
The applicable entries are p. 142 of the DMG for Drow-made gear:
and p. 150 for Adamantine Armor:
Note that the description of the latter says nothing about who made it, or whether it's sunlight-sensitive or not, so it's rather safe to assume it's not sunlight sensitive by default. Double-check with your DM, of course, though!