I then turned my attention to writing the best possible mutation table, which I've posted
and now I'm going to talk about the design process because that's what you do with a blog.
So, Mutations. . .
(1) Yes, you could make a mutation table that was small and/or linear. Like a mutation track for turning into a fish man. But they're usually random, with dozens, hundreds, or thousands of entries. Mutations are essentially chaotic, a fact supported by both biology and Warhammer. The less predictable mutations are, the more genuine it feels.
(2) And while mutations are often cosmetic (new skin color), others are very impactful, conferring new abilities or slaying characters directly.
Most games "play to find out"--we roll dice during combat to for the sake of emergence--but games vary in how impactful they are. Some games limit you to the boundaries of the arena, while others are happy to let you kill your characters, turn important NPCs into bee swarms, and/or sink a continent.
Those two traits (random, impactful) are also shared by the the Deck of Many Things. People who hate the Deck of Many Things also tend to hate random mutations, because both can derail an expected adventure so quickly.
(3) And mutation tables tend to be modular. They aren't bolted onto any other subsystems, and don't usually depend on a particular setting.
People have written some good ones: slack ratchet, Scrap Princess, Skerples
How Big Should a Mutation Table Be?
A small mutation table (< 100 entries) will tend to have more good entries, and less chaff.
A large mutation table (> 100 entries) will tend to feel more random, and have enough variety to please Nurgle.
That's basically my justification for writing a d100 table. I'd love to write a d1000 table, just for the bragging rights, but around 150 entries I started found myself writing down some mediocre entries. There's a sweet spot, I think.
How Lethal (and Beneficial) Should a Mutation Table Be?
That's a great question. I originally had it right in the middle: 30% good, 40% neutral/cosmetic, and 30% bad.
I went on to split the bad into 20% bad, 10% lethal, because I really like the idea of someone losing their ability to breath air in the middle of combat, or burning a hole through the floor as they die painfully.
Mutations should be rewarding enough for players to be tempted, and dangerous enough for them to be reluctant.
So if the worst possible result is basically just death, how good should be best result be? Originally I had a couple entries that were basically just superpowers. Those have been toned down or removed.