Sorry for coming in late, but I only recently bought the Dragon Compendium. I was happy to see the elemental demons made it in the book since I've used them extensively with my gnoll summoner villain. I noticed a few errors or puzzling elements however:
Errors:
- Ash demon: Missing 9 skill ranks. Going by their description, I would suggest Bluff, which would change their skill line to: Bluff +9, Intimidate +11 (synergy with Bluff)
- Ash demon: No HD advancement. It's the only demon with 'By character class' as the advancement
Possible errors:
- all demons: In the Combat section, they are the missing the line saying that their weapons are treated as chaotic- and evil-aligned. Is that deliberate?
- Air demon/Ash demon: Their DR is 5/magic. That seems a bit weak, given that even lowly dretches get DR 5/cold iron or good.
- Fire demon/Ice demon: Their DR is 10/lawful. No other SRD demon has DR lawful. DR 10/good would seem more natural.
As a side note for DMs who would like to use the elemental demons in your campaign, the Final Strike feat from Savage Species would be especially appropriate for them. It requires an elemental subtype, and causes the creature to explode in a blast of elemental energy upon death, with a secondary effect that varies according to subtype. Either replace one of the demons' existing feats, or add it as a bonus feat.