This spell allows the caster to assume the form of a normal or giant animal.
Animals are a type of monster that includes apes, rock baboons, bats, bears, boars, camels, cats, crocodiles, dogs, elephants, ferrets, fish, hawks, herd animals, horses, lizards, mules, octopuses, rats, rhinoceroses, shark, shrews, snakes, squids, toads, weasels, whales, wolves, and any other creatures of sub-human intelligence that occur in the real world. Giant animals are merely larger version of normal animals, and therefore part of this type. Prehistoric animals, such as cave bears, dinosaurs, mastodons, saber-toothed tigers, and titanothere are also animals.
Are all the animals (and their giant versions) listed in the ACKS corebook fair game?
All monsters of the "animal" type are fair game. Note that oozes and vermins are not animals.
Are prehistoric creatures yet another category of animal that doesn't qualify?
Prehistoric creatures do qualify. However, I would require that the character (not the player) know such a creature existed in order to transform into it. I would also require that at least one specimen of the species be still alive in some "lost continent" somewhere, so that no extinct animals would be permitted.
If you think this makes the spell too powerful, you could rule that certain prehistoric animals were actually prehistoric fantastic creatures if you think that's more appropriate. E.g. you could treat dinosaurs as prehistoric dragons. That would exclude them from the spell's effect.
Even if it is just animals, does this mean for a pirate adventure, I can skinchange into a sperm whale (which is a "normal animal")
Yes, you can change into a sperm whale.
Note that since the caster acquires the physical characteristics of the animal, the skinchanged caster will probably not be able to speak and certainly cannot cast spells. At best, transforming into a parrot might allow him to speak, and transforming into a chimpanzee might allow him to use certain equipment.
Still, it's a great spell. It's quite fun to turn into a sparrow, fly behind the enemy, then turn into an elephant and trample them. I'm not sure it's more effective than just fireballing them, but it's fun.
One other question: how do you determine what kind of animals the character can know to turn into? Does the spell front load your awareness of ‘normal animals’ so you can automatically turn into those things, or do you need to have seen an elephant/wolf/giant otter before you can become one?
Further, do you need to study the animal (like up close or a corpse) or simply seeing it once allow you to transform into it?
I’ve been limiting it to animals the character has likely seen or heard about (especially since they got it through Apostasy rather than being a Shaman), so the character has been limited to temperate climate animals and the ones they’ve encountered in game. If they pick up Naturalism I’m saying they also get the common animals from that territory.
I guess I’m hesitant to let it work like 3E Wildshape where players assumed they had an encyclopedic knowledge of every animal in the monster manual just…because.
Great question. I definitely would not assume that the spell gives you any knowledge of animals, no. That’s the road to madness.
If you need an objective way of handling you might try something like this:
Reference the Wandering Monsters in the Wilderness table, Subtable: Animals
Select 2 terrain types representative of the character’s background and upbringing. These are the animals the character is intimately familiar with.
Select 2 terrain types representative of environments quite unfamiliar to the character. (Prehistoric and one other). These are animals the character would have to encounter in-game to be able to transform into as he’s not familiar with them at all (unless they are on the prior list).
All other animals the character can transform into if he makes a Naturalism proficiency throw 11+ to remember them, or encounters them in game.
Ignore any references to monsters that don’t count as animals (such as spiders).
EXAMPLE: Shem is a desert shaman. He is intimately familiar with barrens and deserts, so he can transform into Antelope, Camel, Cave Bear, Dire Wolf, Eagle, Gecko Lizard, Giant Hawk, Hawk, Lion, Mountain Lion, Pit Viper, Rattler, Rock Baboon, Tuatara Lizard, Vulture, Wild Dog, and Wild Goat. He is unfamiliar with Prehistoric and Jungle and cannot transform into animals such as Boar, Giant Shrew, Python, Mastodon, Monkey, Spitting Cobra, or Tyrannosaurus.