It doesn't work. Rebuke is based on cleric level, not domain. As for necromancy spells, well, there's ray of enfeeblement at lv 1 and then nothing.
I have to ask you to either make it more usefull or remove it all togheter. In particular because pseudo-spellcaster already confuses several people, so pseudo-pseudo spellcaster doesn't work that well. May I sugest simply doing pseudo-spellcaster but you can only cast necro spells but stacks with turn/rebuke undead?(so you have right away acess to high lev necromancy instead of just ray of enfeeblement).
He's not the only one. The inevitable, ethergaunt, solar, mind flayer and others also have to deal with mad.
The angel of decay on the other hand can afford to ditch con and get spare points for his other ability scores, and you even give her plenty of ability bonus.
So please just +wis bonus and then increasing with size.
Speaking of wich, made a major buff on the inevitable. it had some SLAs missing, upgraded the chains and gave it a good str bonus so it can be a proper melee dude.
Also gave the dryad good reflex saves since it looked a little weaker than all the other feys.
Hyudra:Wonderfull work with the frost giant! You're really in a roll there! But yes it does seems kinda on the overpowered side. I sugest nerfing all the "no save, just suck!" abilities, like blindness, deafness and ability damage to allowing saves.
I would also make it able to inflict those status in creatures normally immune to it since his abilities are based on raw destruction.