The CR 3 oakman is a Chaotic Neutral fey that epitomizes the idea of "Chaotic Jackass"...but without trying to shoehorn them as Chaotic Good! Bravo, writers, bravo. Now if you'd only done the same with the mimi...
In any case, as their name implies, oakmen are goblin-like male fey that are the spirits of oak trees. Our sage friends say that they might be the male equivalent of the dryads and that their curmudgeonry drives the dryads to seek human mates, but as with most sage comments this is a supposition rather than a fact (read: the Dungeon Master can take it or leave it). What is known is that no sane Druid would want to associate with oakmen. They're rude, crude, lewd, and generally dickish, sitting on their oak branches all day while insulting and demeaning passersby. The only time they get off their branch is to feed humans magical moss cakes that can perform any number of effects from changing the consumer's skin color to causing 1d4 hours of gut-wrenching pain. Lovely.
Remember the orog and ogrillion? Well, meet the ogren, a hybrid of ogre and hobgoblin! The ogren are a culture of rule-by-the-strongest warriors – aren't they always? – that have a savoring for elf and human blood, even going so far as to have blood sacrifices of the two species at their intertribal weddings known as "Takings".
Combining the best of both worlds, the CR 1 ogren is strong and steady (+6 Strength and +4 Constitution) like an ogre and as intelligent and clever as a hobgoblin, if a bit uncouth (-2 to Charisma). Basically, they're what you want as a DM desiring a clever and powerful warring species or a player wanting to play a rather strong species without intelligence penalties.
Remember the fire crab and fire whale from earlier in this very book? Remember how I stated my confusion at the Plane of Fire basically being "the ocean, but burning-pain-oh-gods-so-much-pain"? Yeeeeah...
The oil shark does at least have some ecology to it, I guess. Packs of them will hunt fire whales, volcano giants find them tasty, and salamanders make slick armor (+5 bonus to Escape Artist checks and immunity to webs and similar obsctructions) from their oily hides.