From NWN2Wiki

Devils, also known as "Baatezu," are outsiders native to the lawful evil-aligned plane of Baator. Unlike demons, devils maintain a strict and brutal hierarchy, with Archdevils at the top each ruling over one of the Nine Hells. They are locked in the eternal Blood War with the demons.

Traits

Most devils possess the following traits:

• Immunity to fire and poison.
• Resistance to acid 10 and cold 10.
• Darkvision: All baatezu can see perfectly in darkness of any kind, even that created by a deeper darkness spell.
• Summon Baatezu (Sp): Baatezu share the ability to summon others of their kind (the success chance and type of baatezu summoned are noted in each monster description).

Devils in NWN2

Neverwinter Nights 2 features the following devils:

• Erinyes
• Horned devil (or "cornugon")
• Imp
• Pit fiend

One devil in particular plays a minor role in the NWN2 main storyline, Mephasm, first met as a servant of the warlock Ammon Jerro.