The Shadow in the SeaSource Inner Sea Gods pg. 320 (Amazon)
Pathfinder Wiki Dagon
Pantheon Demon Lords
Areas of Concern Deformity, sea monsters, the sea
Domains Chaos, Destruction, Evil, Water
Subdomains Catastrophe, Demon (Chaos), Demon (Evil), Oceans, Rage
Favored Weapon Trident
Symbol Eye surrounded by runes
Sacred Animal(s) Fish
Sacred Color(s) Blue, gold
ObedienceOffer a bowl of fresh blood to Dagon by speaking prayers over the blood and then emptying the blood into the sea. The bowl must be made of gold and inscribed with runes sacred to Dagon—such a bowl must be worth no less than 100 gp, but can be reused for multiple obediences. Gain a +4 profane bonus against the extraordinary or supernatural attacks of creatures with the aquatic or water subtype.
DemoniacSource Book of the Damned - Volume 2: Lords of Chaos pg. 14
1: First Oath (Sp) speak with animals (aquatic animals only) 3/ day, disfiguring touch (see page 48) 2/day, or summon monster III (aquatic creatures only) 1/day
2: Second Oath (Ex) You become immune to damage from water pressure, and gain the ability to breathe water, a +2 profane bonus to Constitution, and a swim speed equal to your base land speed (or increase your current swim speed by 30 ft.).
3: Third Oath (Sp) Dominate monster 1/day (aquatic creatures only).
For Followers of Dagon