The Pathfinder Bestiary, and the long line of monstrous encyclopedia that came before it, do a great job of attacking the problem of providing game statistics and mechanical information for a very wide variety of creatures. There are a lot of strange creatures from fantasy novels and movies, from ancient mythology, and, as time went on, from the twisted minds of game designers and even GMs, for that matter. Anyone today who tried to go about creating an extensive bestiary of all the different cool and interesting fantasy monsters could fill three or four volumes with three hundred monsters each, and still have a long way left to go, with fans crying out for various "forgotten" monsters to get some attention. That kind of breadth doesn't leave a whole lot of room for depth, and that's where Exotic Encounters comes in.
There are all kinds of reasons why you might not want to use a monster stat-block straight from the core rules. For one thing, if your players have a habit of browsing through such books, or are long-time veterans who know the basic ins and outs of most fantasy staples, you may need an unusual stat-block just to throw them a curve ball and teach them that they can't count on their out of character knowledge to take all the mystery out of the game. Alternatively, many GMs can recall a time when they wanted to make use of a certain monster in their game, only to find that it was a few CRs too high or low for what they had in mind.
Exotic Encounters takes a single, iconic monster, and creates three new variants on that theme. These variants aren't simple tweaks, and are more than simply advancing or removing Hit Dice, though that occurs as well. Each of these three variations on the monster's theme has a specific, flavorful goal in mind, and a role to play, and their statistics entries are gently massaged in order to make them fit those roles. Further, each of these variants comes with brand new specially-crafted special abilities, which are unique to Exotic Encounters and not found anywhere else.
This particular installment of Exotic Encounters focuses on the oft-overlooked ettin. These two-headed giants are capable of being more than just a particularly ugly-looking substitute for an ogre, and have a rich history in both mythology and fantasy games and media. This book introduces three new ettins, the first of which is the primal ettin (CR 8). This monstrous giant is far more feral even than a normal ettin, and its heads are like those of giant boars. Its favored tactic is to impale foes on its tusks and literally rip them apart between its two heads. The next ettin is the ettin mage (CR 11), which trades in superior two-weapon fighting ability for the power to cast spells. Not much brighter than a normal ettin, the one-two punch of flail and magic can still make it a formidable foe, when it can stop arguing with itself. Finally, the three-headed ettin (CR 13) is exactly what it sounds like, and more. This ettin's extra extra head gives it all the brainpower it needs for cunning tactics, making it a supremely powerful foe…unless its heads are picked off one by one.