Picking the Mad Scientist seed could mean that there is a single prominent scientist that is threatening to destabilize society or that there are going to be many scientists that the player group will encounter.
Victor Frankenstein is probably the original template for a mad scientist. He builds his creature without really considering what the consequences are. He also has found a way to harness the power of electricity. Nikola Tesla is also an excellent real life model of the “mad” scientist. He was undeniably a genius but his habit of proclaiming he could build death rays and earthquake machines made him seem unstable and a threat. Tesla stated repeatedly that by making terrifying weapons he would make war impossible to wage. Many inventors of the time felt this way, that by inventing a horrific device it would prevent war. Historically only the atom bomb was so horrible that it was difficult for nations to accept using it but it provides a motivation for a mad scientists of the age. The mad scientist is only concerned with his ability to master creation with his intellect.
In most instances, the classic mad scientist frequently has a mastery of the use of electricity. In the Victorian age, electricity is exotic and little understood. To be able to command and control it is such a feat that it requires nearly superhuman intelligence.
The mad scientist is often in conflict with the rest of society because of the danger their actions pose to the health and well being or accepted norms of the day. The player characters may be acting as protectors of the populous or they may themselves be threatened by the Mad Scientist’s actions.
If there is only one main Mad Scientist, they should be built similarly to a PC but with 40 Story plus 20 for every player character.
Normally a player characters can only invest 6-10 points into an invention at creation. NPC characters can have as many of their SP spent on inventions as the GM wishes. In addition they may have several inventions instead of a single invention.
A Mad Scientist should have a very high Intelligence attribute. They may be very eloquent and lucid but in some situations they may seem babbling and incoherent. This is a style choice made by the GM. Intelligent and lucid maniacs need much stronger motivations than ones that are merely driven mad by power.
For a different take on the mad scientist, there is the misunderstood genius. A good example of this is in the story The Cronic Argo where the scientist is simply minding his own business but his seclusion makes society fear him as being malevolent.