Welcome to Oceans of Blood, the sixth in our line of monster books called Mythic Menagerie. Each volume in this line presents a small set of monsters tied to a single theme, but spread over a range of CRs. For Oceans of Blood, the theme is threats of the sea, with an emphasis on monsters that bite, tear, and rend. Author Sam Hing has created aquatic adversaries ranging from the mindless CR 1 harpoon weed and razor shoal to the incomprehensible CR 14 anemone behemoth, with enough surprises in-between to spice up seaborne adventures of any level.
Oceangoing adventures have a long and famous history in adventure stories, from the Greek legends of the Odyssey or Jason and the Argonauts to the modern terrors of Poseidon Adventure and Jaws. Adventures at sea are often rife with exploration and horror, likely because the sea was the best known "final frontier" for centuries, representing a place in which you could get lost easily, find new things, or get killed just for visiting. We are creatures of the land, and the threats of the sea are always going to be a little stranger, and thus more frightening because of that.
GMs can find it difficult to simulate that fear in a roleplaying game setting where fireballs are common and raise dead is an option (although reading and enforcing the rules for stealth and detection underwater as well as underwater combat in Chapter 13: The Environment of the Pathfinder Roleplaying Game Core Rulebook is a good start). This is especially true for experienced players, who can identify an aboleth from a single vague sentence and quote the differences between merfolk and sahuagin by heart. So more than any environment, the untold depths of the vast oceans are begging to be inhabited by new, strange, and (for player and character alike) previously unknown threats that can get fear flowing once more. And that's enough to make any GM smile.
We're confident that you'll find something useful in this, our sixth Mythic Menagerie. We have chummed the pages to draw out the nastiest of swimming slayers, and they're ready to make your players afraid to go back to the beach. Dive in, and see how warm the red waters are.