Fat Jim is the first major boss in Jim of the Floating Isles. Similar to Jim, he too is not given a special name and his name is a species, not just one. His voice is actually a little bit high pitched, except when he's mad his voice is in G Major.
When you find him, he is having a fit on an isle big enough for him. He spots you and chases you, which does a mini level when your running away from him. At the end, the Sign Spirit lifts you to a large isle, telling that the Fat Jim ate the Magnetic Switch. The Fat Jim jumps there and the real battle begins. You have to use the enemies to follow you causing them to get in his fur making him itch. There, you can hop on his belly causing him to get a little sick. Sick enough, he starts crying and sneezes out the Magnetic Switch. It turns out he was having a fit because he got a lot of Titan Bamboo for his birthday, and it got crushed when the world departed. The Sign Spirit instantly shoots Titan Bamboo seeds which instantly start to grow, and Jim hops on the Sign Spirit so he doesn't get crushed. The Titan Bamboo begins shooting out more seeds as the Sign Spirit puts more land together with the Magnetic Switch. The land then touches the ground, and Fat Jim is safe.
In Later Levels
In the first level of the Final isles, volcano, he helps by crushing rocks in his way. In the final boss, he tackles the main enemy causing Jim to be able to flee real quick. In the end, he is hurt pretty bad, but wakes up to the smell of the Titan Bamboo now that the entire world is placed back together. In the credits, he can be seen riding a slow moving parade car eating some of his Titan Bamboo.
In appearance, he is about 1/8 the size of the mighty Titan Jim. He is orange in color, with very spiky side furs and the feet are flat. When chewing, he is revealed to have two large teeth, one on the top and one on the bottom which join to eat the most toughest things of his meal. His thighs are similar to a dog's- curved, and covered in lots of fur. He does not have legs, but only feet. When you are fighting him, he is bright red, and his eyes are glowing yellow, giving steam as well.
- A similar idea was going to be used in Range! Aim! War! before it was canceled. The enemies managed to put a brain probe on his head causing him to the first boss, but when defeated, they made it up to him by giving him a lot of Titan Bamboo. He then helped in the next level by crushing wooden walls in the river, only to be distracted by the enemy's planted poisoned Titan Bamboo, which the units must destroy.