If you have LA buyoff allowed
Feytouched 0/Half-fey
Transition 1 (buy off at 3) /
Half fiend 2 (buy off at 6 and 9)That nets a total SLA list of
Charm person at will, faerie fire or glitterdust 1/day, hypnotism 1/day
Detect law 3/day, enthrall or sleep 1/day
Protection from law 3/day
Confusion or emotion 1/day
Eyebite or lesser geas 1/day
Darkness 3/day
Poison 3/day
Desecrate 1/day
Unholy blight 1/day
Along with
Str +2, Dex +2, Con +2,Wis +2, Cha +2, immunity to enchantments, wings, natural armor +1, 2 claws, darkvision 60 ft., outsider type, bite, poison immunity, resistances (acid 5, cold 5, electricity 5, fire 5), spell resistance (equal to character level).
For a +CR of either 0 or 2, depending upon how you count bought-off LA towards CR. In either case, you've got a nasty evil overlord pseudo spell list, a nasty set of demonic natural abilities, and stat boosts to everything except intelligence.
Dropping the second half-fiend transition level is possible, since the cooler abilities are granted by the first level.
Add that onto a dread necromancer going into prestige paladin of slaughter/tyranny., and you've got an intimidating baddy that isn't going to easily WTFcurbstomp the party.