Table of Contents
Animal Tips
Testing Cow and Pig forms as a Demo Player
I don't recommend that demo players play as animals since you are not able to visit Animal Town in Sun Vale and a lot of the NPCs in Serbule seem to either hate or want to eat you if you are one. That said, there are some ways you can “dip your toes” into experimenting as a few animal forms in the game even in the demo. Just keep in mind this is a “hard mode” of sorts, because once you go Pig or Cow, you will NOT be able to easily change back. This section only exists to explain how it is possible to get back, but these means are by no way easy or cheap ways to go back to being human.
Cow
One option to consider is Cow form. Once you are level 15 or so in combat and you've progressed to the point where you have access to the Crystal Cavern, you should be able get to a mad cow named Maronessa deep in the cave. She's been the result of some nasty Davos experiments, and can dish out some serious damage for an early boss. If you turn and run away after she hits you a few times, you will notice you have a debuff that will eventually turn you into Cow form after about two minutes.
Pig
Pig form doesn't have an easy way to become one, but you can buy Ruggedizer potions from Charles Thompson or sometimes find Pig Potions on either Charles, Marna, or Mushroom Jack (Buy Used or Consignment). If you have the money, Ruggedizer has a very small chance to turn you into a Pig, but after about 20 of them, you might find you become one.
Reverting back to Human
For Cow, there are only three options for returning to human form that I know of. One is to get your Cow and either Psychology or Unarmed combat skills high enough that you can take out Maronessa. While Maronessa is certainly tough, it's even tougher to deal with the poisonous slugs along the way. If you have the ability to make Poison Resistance potions, they are a lifesaver here.
The second way for Cow is to talk to Harry the Wolf who will give you a way to undo Cow for 30 Grass, 5 Milks, and a whopping 50 mushrooms. This might be a one-time quest, I'm not sure.
For Pig, there are really only two options, but only one of them is relatively easy and cheap. The other harder one is the UnPig potion which you can get from killing Pigs. After about 100 of them, you should find a potion to “Unpig”.
For both Cow and Pig, there is yet another way to undo your animal forms, and it's probably the easiest. You can use a Word of Power (level 0 for Cow, Word of Power III for Pig) that you should get as an ability from the Lore skill.
For Cow, you can get this skill just by looking at books and things in the house Marna is in. It is important to note that while this is easy and cheap to do, it's still pretty damn rare to get a SPECIFIC word of power, so be prepared to go through quite a bit of Crab Meat trying. You can get the ability to remove meat from the Crabs from Fainor for only 80 councils, but in order for him to talk to you, he might want you to do something or give him more money at first.
For Pig, the Word of Power 3 skill requires a pretty rare item called Evil Grass and two other rare/expensive items to find. These items as a whole are so difficult to get it is probably easier to find or purchase an UnPig potion.
In both cases, I'd still highly recommend purchasing the full game if you want to get a more robust Animal experience and have access to a town designed for their safety and support in Sun Vale.
Strange Pig and Bunny Event
It is worth noting that there is a Strange Pig event in the game that lets you easily test the waters as other animal forms as well. On the north side of Serbule Keep, just across the bridge, an NPC named Norbert from Animal Town will sometimes come visit to let players easily turn back and forth between different animal forms. This is another way to test playing as an animal without making a hard commit. There's also a Bunny event that works similarly, but this only happens about once per year around Easter time.
Playing as a Cow
As a Cow, you will find that you get a lot of abilities that compliment Unarmed or work well with Unarmed. This is because Cows fulfill the role of Tank and are meant to get up next to the enemies they are attacking.
They also have very powerful Kick abilities and can use them with Unarmed or other mods that give bonuses to kicks. Additionally, all Cows are considered female, so you might find players coming up every so often attempting to Milk you. You can choose to allow this or not.
Lastly, Cows get a pretty neat option to use Grass to heal themselves, they can also collect grass with a Graze ability. Note that the ability to consistently Milk yourself generally requires that you gain and retain the “Vegetarian” badge and stay away from foods that contain meat in them.
Cows are a great “tank” class to play if you have a friend that can DPS or one that can heal you.
Official Wiki
Playing as a Pig
As a Pig, you get a lot of abilities that affect everyone in your party or those around you. Pigs can dish out and take some small amounts of damage, but it's not generally recommended to take them as a Tank or DPS class. In fact, one of the strongest healing combos in the game is a combination of Pig and Priest, so you may find it's easier to focus on having them be a healer. You won't be able to play as a Priest in the demo, however, so I would recommend Pig/Mentalism or Pig/Psychology if you want to play as a group healer and buffer.
Pig can be a really good class to play if you have a Cow Tank friend who is playing Project Gorgon with you or a group of friends that want to have a good buffing support class around. It does somewhat limit you to focus as a healer only as a first-time player, so you will have difficulties trying to solo as this class. Lastly, Pigs do get an ability to sniff out mushrooms every few minutes that match the zone they are in. This can be very powerful in high level zones where it would otherwise be difficult to do such tasks.
Official Wiki
Make a Second Human Character
If you are committed to playing as a Pig or Cow during the demo, I would recommend making a second character to use as a “mule” or a play to store extra inventory items by using the “Account Storage” chest as a transfer mechanism next to Hulon in Serbule. Get this second human or humanoid (Rakhasa, Elf, Human) character through Anagoge Island to Serbule as quick as you can and keep its inventory relatively clear for these extra items. Later on, after you've paid for the game, you can buy pocket gear for this mule character to store even more items.
Spider, Spirit Fox, Giant Bat
I don't really have experience with these classes, but it might be possible in certain circumstances to become these even as a demo character through in-game events or with the help of other players, so I did want to mention them here. I'm not encouraging being these classes at all.
One in particular that is certainly possible with help in the Serbule Crypt is the Spider class, but again, without access to Animal Town, you're going to be very limited in what you can do and won't have much support in the demo-accessible zones.
Giant Bat would require another player with Giant Bat bite you in the PVP “basement” arena accessible through a specific house in Serbule.
Spirit Fox you can accidentally or intentionally get by giving a Spirit Stone to a Spirit Fox NPC or player. It's not cheap to do this and again, highly NOT recommended as a demo player as this is essentially a one-way trip to being a Fox pretty much forever as a demo character and you won't have access to Animal town. Still, you should probably know a little bit about this if you are interested so I'm mentioning it here.
It should be mentioned that even some animals are distrusting of Spiders and Giant Bats, so if you go this route in the game, be prepared for less NPC interactions. My understanding from talking to some of the Bats and Spiders is that the tradeoff for less NPCs liking you is that you do kind of get access to some really powerful abilities and damage output among Giant Bats and Spiders in the late game is quite high for specific builds. Spiders do get an ability to temporarily look like a human, but that ability has a very long cooldown.
Official Wiki
Deer as Druid
There is a way to test out Deer as a Druid, but as a demo player this isn't really an option. Still, this is worth mentioning, as if you get the full game you can rely on just getting a single skill to combat level 50, then you can use the Druid alter in Sun Vale near the big tree to actually go Druid. There might also be a Word of Power to become or unbecome a Deer. Eltibule has a vendor who sells potions to undo Deer, too, though it's not very cheap.
Other Links
There's an animal guide I found randomly online for Project Gorgon here as well: https://www.riotbits.com/project-gorgon-animal-survival-guide-35916/