The one-species rare but powerful Fire Jim is the most lethal enemy in the entire Jim of the Floating Isles, even more then the final boss, however, it is the most defenseless. On the final level before the Magnetic Plug stage in the Desert Isles, near the end is one single, slightly bigger red Jim with some Pyrojims are on the edge of a floating isle. If Jim gets too close, the Fire Jim bursts a wall of flame, easily avoided, but lethal. The Fire Jim does not turn, so after beating the Pyrojims, you can easily kill the Fire Jim, who has but one health point.
The player is often confused for a second as to think he is a Pyrojim. But if you notice, a Fire Jim is a tad bigger and its fur is pure red, not with an orange mix. The Fire Jim is not technically a boss, but you may consider him when it comes to having to fight nearby.