An ex-druid 1 / chameleon (Races of Destiny) wants to take levels in blighter (Complete Divine). Can he?
A level 1 ex-druid with the prestige class chameleon (Races of Destiny 111-7) that once used the extraordinary ability aptitude focus to gain divine focus to cast druid spells and that has Wisdom 16 (if a 3rd-level chameleon) or Wisdom 13 (if a 4th-level chameleon) so that it can meet the blighter prerequisite of being able to cast 3rd-level druid spells could possibly take levels in blighter (Complete Divine 23-6).
The blighter's special requirement says, "The character must be an ex-druid previously capable of casting 3rd-level druid spells" (CD 23), and those statements aren't independent. Thus the DM may require the chameleon to be, instead of a 1st-level ex-druid, a 5th-level ex-druid, the minimum druid level for casting 3rd-level druid spells.
Also, the prestige class chameleon on Class Features says, "You can’t use any abilities gained from your aptitude focus… to qualify for a… prestige class" (Races of Destiny 112). So the player must make the argument that—and here I suggest first buying pizza if not good booze—using the absence of something to meet the prestige class's requirement is different from using the thing itself to meet the prestige class's requirement. I can't imagine such an argument working in most circles without the booze; stay safe and good luck.
(When composing this answer initially, I—like, I'm sure, many others—overlooked that chameleon Class Features text; thanks to this answer for pointing it out.)
Races of Destiny, page 112:
You can't use any abilities gained from your aptitude focus, ability boon, or mimic class feature abilities to qualify for a feat, prestige class, or other option.
Were it not for this frequently-overlooked bit of text, the other answers would be correct. Alas...
Yes. Any race or class that can meet the requirements1 would work.
With Chameleon, specifically, you would require:
Divine Focus: You gain the ability to prepare and cast divine spells, which may be chosen from the spell list of any divine spell-casting class.
And of course, have the Chameleon level required to cast 3rd level spells. Could the Chameleon cast 3rd level druid spells? Yes, they can.
- Base Attack Bonus: +4
- Alignment: Any nongood
- Special: The character must be an ex-druid previously capable of casting 3rd-level druid spells, Profession skill must be herbalist.