Personally I find mutagens obnoxious. They’re highly unreliable even with the Robust Genetics trait, and the system is almost too complex understand (read: it takes serious study effort). On top of that, making mutagens requires skill, effort and resources. Here’s what I’m suggesting instead:
We make targeted and trait-specific mutagens and get rid of mutation trees altogether. So instead of spider mutagens we’d have Night-Vision mutagens and Runner mutagens, for example. Each mutagen would also come with an inherent success rate, in 5% increments, so for example we’d have Night Vision mutagen (40%) and Night Vision mutagen (85%). Failure would result in a negative trait. Potential negative traits for a mutagen type would be listed separately in game files, so failure from Night Vision mutagen could result in Bulging Eyes or Light Sensitivity. Additionally, the success chance for each mutagen could be hidden, until the mutagen/serum is analyzed, possibly at a centrifuge, or with a portable tool. Accurate analysis could require Cooking skill, so low level chemists would get results like 50-90% for mutagens that actually have 80% success rate. The lower the skill, the higher the variation for each analysis. Of course you could drink unanalyzed mutagens if you wanted to.
Alternatively, mutagens could have separate success AND failure rates. So for example a mutagen could have
50% success
20% failure
30% no effect
or how about
10% success
5% failure
85% no effect
The gamble should be more clear at that point.
