At some point I may extend this post to do a whole write up on the Demiplane of Nightmares (I enjoy the freedom of detailing demiplanes) but for now I’d like to stick with debating the abilities of a Diabolus so here goes.
Some explanations for my thinking first though. I wanted to carefully balance the race with what’s in Monsters of the Multiverse but also hold true to their origins as much as possible.
The tail was easy to do, but the immunity to magic from Prime casters would’ve made a Diabolus unplayable (as would primes being immune to their magic). I hope what you see below is a reasonable compromise.
Diabolus as a playable race in 5E
by SeethyrOften mistaken for devils, demons or at the very best tieflings, the diaboli are a race of humanoids native to the Demiplane of Nightmares and they have more in common with mankind than they do any sort of fiend.
Diaboli have cloven feet like a goat, tiny horns and a tail that ends in a barb. Their skin color is often described as mauve but it can range from lighter purples to black in coloration. They are also four fingered and are described as having reptilian eyes and a sibilant, forked tongue.
Diabolus Traits
As a diabolus, you have the following traits.
Creature Type. You are a Humanoid.
Size. You are Medium.
Speed. Your walking speed is 30 feet.
Darkvision. You have darkvision with a range of 60 feet.
Tail Barb. You may attack with your tail barb causing 1d6 + Strength modifier in piercing damage instead of the normal bludgeoning damage from an unarmed attack.
Resistance of the Nightmare Realm. Your nature as a native of the Demiplane of Nightmares gives you some resistance to the magic of creatures from other planes. If you fail a saving throw against a magical spell or effect cast upon you from a creature that is not native to the Demiplane of Nightmares, you may choose to succeed instead as a reaction. You may use this ability a number of times equal to your proficiency bonus between long rests.
As optional traits using the original 5e system which seems to be disappearing I’d add these.
Let me know if you think the collection of ability score increases should be different. I don’t know exactly why I chose Con and Wis, it just seemed to fit the Diabolus.
Ability Score Increase. Your Constitution score increases by 2 and your Wisdom score increases by 1.
Alignment. You appreciate chaos though you still often follow a strict code of honor. Your alignment tends towards chaotic good.
Languages. You can speak, read and write Diabolan and Common.