True, Ur-Priest could be a bit of an issue. I don't think anyone was planning on taking it, though, so it isn't a problem yet.
Also, it turns out I was wrong on the Ogre Magi's overall CR, so you actually would have room for a +1 CR template for that particular character. ^^
Yeah, if I take route where I take 11 levels (+5 1.5 CR, round down?) and so have CR 13 with ogre magi stuff and have 16 HD. So 1 CR play with. My original idea was sort of take warlock level (for will save) and then ur-priest 2 levels and then go eldricth theurge 8 levels (so invocations as 9th level warlock and 10th level ur-priest casting which provides 9th level spells). But I stepped back from the idea (because it's cheesy perhaps exploit ur-priest) and picked different classes.
Unless we go by this article
changes or analysis. I myself would be happy we drop ogre magi to CR 5 as it is (no changes done to race but drop CR because according article ogre magi CR is over budgeted) but that needs ST decision/approval.
Okay, here comes my concept (for GM approval, as he needed bit description and personality along with build idea for approval right? I used CR 5 base for ogre magi and add +1 extra HD as giant to get 16 HD filled)Vholdran, the seer of Abyss
(monster of legend ogre magi prophet prodigy (int&cha) diviner 3/master specialist 1/divine oracle 6)
Vholdran has been a curious sort of ogre magi; he was born very frail and weak compared most ogre magi but what he lacked in physical might he made up with his mind instead. He was most cunning and charismatic ogre in the ogre tribe and he used his influence and charisma manipulate others to do his bidding. More so when he started get visions
from the future. Since then he has entirely depended on his curious gift as a seer to help guide himself and his goals, ambitious yet sticking to shadows and do dumber people (his clansmen) do all the fighting. However what he thirsted was; more knowledge above all. Eventually his gazes set upon abyss....and then using his visions guide him he entered one dozen portals to abyss and he entered the hellish and chaotic realm which none did not know what happens next, instead he embraced the chaotic energies and his unique gift allowed predict future events quite accurately.
Soon various demons sought his council for future visions and he gave them advice....only those which long run benefited him and him alone. He started gain secrets, form contacts and start trade favors to get higher on ranks in demon society which is ruled by brute power but his cunning and insights into future gave him a edge which surpassed the physical brute strength. So thus many who think ogres just simple brutes get awful surprise when they cross Vholdran who's cunning matches archdevils themselves. Then it came to him, not a surprise at all as he had worked for that goal for several decades, he become demon prince and he knew his position is vulnerable but he also foresaw others who would receive same gift as he did....so he knew in advance where to go and send invitations to other fresh (young) demon lords to gather.....
Edit; Prophet and Prodigy are from DMG II pg157 section (unique abilities). Prodigy is CR 0 but I think they are 1/2 CR (rounded down) so two prodigy is CR +1 CR to individual. With diviner may go for focused specialist and take UA variant for it (take away familiar).