As I've mentioned more than a few times, the cult of Turms Termax was predicated, at least in part, on the notion that the ascended mortal Turms was the greatest of all the gods. Indeed, all the other gods were little more than feeble prefigurations of his perfect plenitude -- "past echoes," if you will. Consequently, once the cult seized full control of the Thulian Empire, it began to systematically co-opt all the sects of the Great Church, teaching that each of the gods they served was an aspect of Turms, whose full majesty could only be appreciated by a select few, namely the "True Spirits" of his cult.
Lesser men cannot grasp Turms in his fullness and thus must content themselves with understanding only a part of him, as mediated through one of the sects dedicated to a god-aspect. To emphasize this point, many representations of the gods had their heads replaced with that of Turms Termax (or, occasionally, his consort Sarana). In Dwimmermount, there are many statues of the gods to be found, almost all of whom have had their heads replaced with that of Turms. Indeed, some of them were even intentionally fashioned that way. Needless to say, this practice wasn't popular with many devotees to the other gods, who were persecuted for their obstinacy and formed the core of the resistance that eventually brought down Termaxian -- and, by extension, Thulian -- rule.
Tales are told that removing the head of Turms Termax from a statue of one of the gods and replacing it with its proper one grants a divine boon. If such tales were true, the strength of the boon would depend on whether a new head were fashioned for the statue or if, by some chance, the original could be found and restored to its former place. Likewise, the gods are often unpredictable when dealing with mortals, meaning that the nature of the boon itself cannot be predicted.
Here is one example pertaining to gods of the Dwimmermount campaign (I'm leaving the others as surprises for my players, after all):
Original Head: Make a saving throw vs. spells. Success grants the one-time ability to turn a failed roll of any type into a success. Failure grants the permanent ability to re-roll any die roll once per day, but the result of the second roll supersedes the first, even if it is worse.
New Head: Make a saving throw vs. spells. Success grants a one-time bonus to any upcoming die roll of the player's choice, with the bonus being equal to the difference between the number needed to save and the actual roll. This not a guarantee of success, however, so the decision to call upon this blessing of Tyche must be made before the dice are thrown. A saving throw roll equal to precisely the number required results in a permanent +1 bonus to one of the following:
1 = To hit rolls
2 = Damage
3 = Armor Class
4 = Initiative
5 = Saving Throws
6 = Reaction