The Doctors Ruby have taken advantage of this wildlife mutation to import and breed them to roam the island. Not good for the local fauna, but they soon deal with any unsuspecting visitors in an environmentally friendly manner.
Land Pirahnas are particularly good at detecting methane.
First thoughts:
AC 12, HD 2, Bite: 2d4, Kick: 1d4, Tail:1d3
Can use claws for minor effect or tails like cudgels if wanting to leap away, which is not very likely in a kill frenzy. Add morale modifiers for that.
In 2042 the supervillian Dr Ruby apparently died. The Superhero 2044 game setting is post a six day nuclear war in 2003 and in 2029 the aliens from Formalhaut arrived.
Dr Ruby destroyed the premier superteam. Ruby was a geologist and comuter scientist of fantastic ability. In their final standoff he threatened nuclear devastation, he instead ended up blowing up Mount Inguri, causing an eruption, killing most of the team and presumably Ruby.
Not so. His forcefield and lava armour let him escape through a prepared tunnel out of the mountain – traces of which vanished in the volcanic eruption.
The good doctor absconded to Lord Howe Island. Unknown to anyone, Dr Ruby was a team. His sister, a talented spy who could pass for the mysterious doctor and an even better computer scientist and physicist had prepared a lair there. Ironically, in a volcanic shield cone.
There, she had made a breakthrough. Time travel. Limited, in that it could only go to one place and only backwards – around as far as a century. So most of the time she had been working on a base for the pair of them – but off the coast of 1830s to be Australia.
Her brother’s antics provided cash and also distracted the Science Police and the Freedom League from finding out about her and her research.
The fantasy 1830 version of such, anyway. Lord Howe Island is an extinct shield cone – much smaller than it used to be. Natural place for an evil villain lair.