I just invent the bonuses I want any given monster/NPC to have in the moment, without the slightest care as to what the stats "should" be according to the rules. Why should I bother with that, I'm the DM!? I'm not going to stop the game for 15 minutes to figure out what a 5th level troll blackguard would be or what have you, I'll just jot down whatever bab, hp, powers, etc I want them to have.
Sometimes I won't even jot it down.
Since my players know that they must not question me, it is never a problem. They feel challenged, and enjoy the game.
The rules are there to control the player, not the GM.
Nisarg