Rainbow Servant
The Rainbow Servant is a prestige class from Dungeons and Dragons Third edition, appearing in the Complete Divine splatbook. It is notable mostly for being abused with Warmage, Beguiler, and Dread Necromancer; otherwise, it's shit.
The Fluff
Couatls, in D&D, are magical, rainbow-colored, flying, lawful good snake-things that spend most of their time hiding in temples in a jungle somewhere, keeping tabs on what the forces of evil are up to but doing very little to stop it. The job of actually stopping the forces of evil gets delegated to their servants: arcane casters who decide they want to learn a little bit of divine magic too, which the couatls are more than happy to teach them. Why do the couatls only accept arcane casters if they only teach divine magic? Why don't they also enhance dedicated divine casters like Clerics and Favored Souls? Fuck you, that's why.
The Crunch
The basic idea behind Rainbow Servant, mechanically, is that it continues the spells known, spells per day, and caster level of the underlying arcane caster class, while periodically adding cleric domains and some random garbage like rainbow-colored wings. At the tenth and final level, it opens up the entire Cleric spell list for the character to learn and cast. In most cases, it does not retroactively teach these spells; the character will need to resume taking levels in wizard or whatever in order to actually learn Cleric spells.
Specifically...
Prerequisites Alignment: Any nonevil and nonchaotic. Skill: Knowledge (arcana) 4 ranks. Spells: Able to cast 3rd-level arcane spells. Special: Must find the hidden jungle temples of the couatls.
Hit die: d4
Skill Points at Each Level: 2 + Int modifier.
BAB: 1/2 of character level, same as wizard and other dedicated casters
Saving throws: Fort and Reflex are poor, but Will is good.
Features:
- At level 1, the character gains the Good cleric domain and the ability to use Detect evil at-will. - At level 4, the character gains the Air cleric domain and sprouts gay rainbow wings that allow a limited form of flight. - At level 7, the character gains the Law cleric domain and the ability to use Detect chaos at-will. - At level 10, the character gains access to the entire motherfucking cleric spell list and the ability to use Detect thoughts at-will. - At all other levels, you can add +1 to the level of your underlying arcane caster class for the purpose of determining your spells per day, spells known (if applicable), and caster level.
Editorial
All right, let's get this out of the way: this class, as it is intended to work, is unmitigated shit. If you build it on top of a Bard, Sorcerer, or Wizard, then the junk you get from levels 1-9 is nowhere near good enough to make up for the delay in your spell progression. Furthermore, while the Cleric Domains are instantly added to your character's abilities, the Cleric spell list isn't; what you're really gaining is access to the Cleric spell list, meaning that in order to actually learn those spells, you usually need to go back and take more levels in your underlying arcane caster class. Since you need a minimum of 5 levels of Wizard, 6 of Sorcerer, or 7 of Bard in order to even qualify for this class in the first place, you'll be able to learn fuck-all from the Cleric list before hitting level 20 and presumably the end of your campaign. Seriously, when played as intended, the most noteworthy thing about this class is that it lets you get gay rainbow wings at a character level of 9, which is a lot better than the 17 levels that Favored Soul would make you slog through but still not the absolute fastest way to get wings.
HOWEVER, there is an itty bitty tiny little loophole that David Noonan did not consider when writing this class. You see, there are some spontaneous arcane casters (Warmage, Beguiler, and Dread Necromancer) who don't bother with "learning" their spells. Instead, they just automatically know every spell on their class spell list. When you stack ten levels of Rainbow Servant on top of one of those classes, "list" becomes "lists", and the entire goddamn Cleric spell list gets dumped straight into that character's brain. This allows them to spontaneously cast any Cleric spell they want, at any time, like a Favored Soul hopped up on methamphetamine and Viagra. This godlike increase in flexibility comes at the cost of delayed access to your highest-level spells, however, so some people argue that it's better to just take 20 straight levels of Cleric, Favored Soul, or whatever arcane class you were planning on building your Rainbow Servant on top of.
Since the prerequisites include the ability to cast arcane spells, rather than just having an arcane caster level, Warlocks and Dragonfire Adepts do not qualify for this prestige class. It would not do them much good if they did.