Overlapping Deity Portfolios [ODP]: When two or more gods share patronage of a specific area, thing or quality.
Officially, PETTY GODS is pro-ODP. Gods who bear similarities to each other will be natural rivals and be a good source of conflict in the campaign. Think of the complicated relationship between Sauron and Saruman.
A perfect example is the case of Grugzaret (created by David Wellington) and Thuf (created by David Haraldson). Both godlets were created independently and without foreknowledge of each other's existence.
"Grugzaret is a god of subterranean darkness, and he despises those who pollute his perfect gloom by striking lights where they are not wanted. Though it is commonly held to be a pointless superstition, many adventurers speak a scrap of nonsense rhyme as they light their torches or lanterns: ‘Ware damp/Snuffer fly/burn true/where shadows lie. This prayer is rarely heeded, though, for the Snuffer has no desire to be placated, only to extinguish lights wherever he encounters them."
"Thuf, Lord of Unexplained Winds in Underground Chambers and Lights Extinguished at Inconvenient Moments, Protector of the Underworld’s Secrets, He Who is Lost but Would Not Be Found."
|"Grugzaret" by Ryan Browning|
Thuf and Grugzaret could be allies, but more likely the patrons of rival underworld cults. Perhaps they are manifestations of a greater god at war within itself. They could be worshiped by very different groups. Whereas Thuf seems like a god of lore and of great interest to magic-users, Grugzaret is less sophisticated and more primal -- a boogeyman worshiped by the little folks who dwell beneath the surface.