Demons, devils, fiends and filler

D&D invented demons, devils and daemons to fill spaces in the alignment grid. While the conflict between the lawful devils and the chaotic fiends did make for an interesting spectacle, the daemons (or yugoloths in later editions) were pretty boring since their entire shtick was being mercenaries for the other two. The distinction was also undermined by the demons and devils lacking any kind of unifying aesthetic or motif. In fact, all three were created using the same random number tables in Appendix D.

Criticism of filler

Pathfinder went even further and introduced a dozen more groups of fiends. These were typically niche or overlapping concepts and rarely had unifying motifs or anything else to distinguish them from the bazillion fiends that already existed. They looked like the result of the same random generation tables and all behaved the same way (kill kill kill!).

In particular:

• Daemons, demons, devils and sahkil look randomly generated.
• Asura, div and rakshasa look vaguely Middle Eastern or Indian, but barely noticeable.
• Demodands are fat frogs.
• Kytons are into mutilation and extreme BDSM.
• Oni wear Japanese oni masks.
• Qlippoth are based on Shub-Niggurath from Call of Cthulhu.

Their various motivations are just variations on killing everything around them. Pathfinder never does anything interesting with them and generally treats them as interchangeable while whining about how unique and special snowflake they are.

Rational distinction

Many writers have criticized this as an unnecessary, arbitrary and anal-retentive distinction. Others have provided suggestions for distinguishing them in a logical and non-arbitrary manner.

• 4e tried to distinguish them by making demons into corrupted elementals and devils into fallen angels. Then WotC sabotaged their own efforts by failing to provide unifying motifs.
• 13th Age provided a list of possible ways to distinguish them while subtly mocking the whole concept of distinguishing demons and devils. Demons are depicted as largely destructive while devils have an entire subgroup of "covert devils" dedicated to subterfuge.
• The Fumanor setting suggests that devils were created by the forces of law to compete with the demons of chaos.
• Blogger eotbeholder suggests that they be distinguished tactically: demons focus on direct results (destroying mortals) whereas devils specialize in manipulation and subterfuge (making mortals destroy themselves). He suggests they both be based on the seven deadly sins.
• Blogger James Young suggests that devils beget sin but embody virtue to behaviorally distinguish them.
• Blog of Holding suggests making devils look like angels to visually distinguish them.

My personal suggestion to pick an aesthetic keyword and stick to it, inspired by the addition of demonic broods in The Slayer's Guide to Demons. If a demon is associated with a particular sin, their aesthetic shows that off just like the demons in Dragon Age. If a demon is associated with a particular brood, that brood has a unifying motif and modus operandi. Much as how you can tell the various kinds of humanoids are relating to those sharing their tag, these unifying motifs may be identified on sight, used to show that different monsters are related, and distinguish the different families from one another.

Speaking of sin-based aesthetics... a fascinating idea I saw proposed by Craig Cochrane at Eternity Publishing was the idea of there being not seven deadly sins, but ten. In addition to the traditional seven (pride, greed, lust, envy, gluttony, wrath and sloth), Craig adds despair, discouragement and vanity. Rather than nine circles of hell, there are ten (similar to Chinese folk religion) with each representing one of the sins and patronized by an associated archfiend. This will feature in my eventual treatment of hell in my campaign setting.

Re-skinning

While reading Creature Collection III: Savage Bestiary I came across a marvelous idea. The book explained that the Scarred Lands campaign setting had two groups of celestials: the heroic custodians and the merciful angels. The various archons and angels presented in the SRD were not tied to one of these, but were general castes which could be found among both by switching their subtype.

Thus, I thought it made perfect sense to apply this to all subtypes: demons, devils, etc. This makes all the monster families instantly more diverse, since the primary distinction between different reskins of a monster is their aesthetic as described to the player characters. After seeing the subtype bloat in the Pathfinder bestiaries, this suggestion is a breath of fresh air.