Essentially, instead of that fur or those horns or whatever crazy growths or changes appear on your body just magically showing up, there should be cool/scary effects that take a bit of time to show up.
First of all, I believe there should be a brief waiting period before mutations actually show up on your body, to account for the fact that the mutagen needs to enter your system first.
Then, the effects occur. For example, if you got the 4 Tentacles mutation, the game would give you a series of messages like so:
“Your fingers begin shrinking into your hands!”
“Your arms grow longer and feel more flexible!”
“Both of your arms double, splitting into tentacles!”
If you got the horns mutation, there might be unpleasant effects as well:
“Horns burst painfully from your head!”
Effectively, you would get to see your character becoming horribly misshapen before your eyes (as much as a roguelike allows you to see, anyway).
It’s not really a game-changer, but it would make the effects of drinking that substance/eating that strange limb more obvious, and far more dramatic.
