I am starting a new game and am toying with an idea of allowing the concept of purchased mutations to add an extra dimension to my game and as I am a novice GM (haven't run a game in 20 years) wanted to get an opinion of more experienced GM's on what they think of the concept and what pros and cons they can see with the idea.
The world I will be setting the adventure on is largely a feral, low tech world with the PC's only playing humans so I thought it might be a good way to make up for not being as powerful as a CSM by allowing the players an extra chance to purchase mutations they like (the normal random mutation rules still apply) by allowing them at a certain corruption threshold to buy mutations at an experience point cost. The threshold I was thinking of was 10, though maybe 20 will be more appropriate. When they reach this threshold they will have an opportunity, in addition to anything that would normally occur at that threshold level, to purchase one mutation either adapted from the mutation chart or from the mutations listed in Whitewolf's Freak Legion: Revolt of the Flesh (and yes I am sure I am showing my age in referencing this).
The players would only be able to purchase the extra mutation at the end of the adventure in which they attained the corruption threshold and it would be a use it or lose it scenario in which the players chose to buy one (and only one) mutation or if they decided to use the experience for other advances or save them then they would not get the option again until they reached the next corruption threshold. I figured this would stop the players from picking endless mutations and not putting their hard-earned experience on other important advances, such as attributes, skills and talents.
At a rough base (that would need a bit more tweaking) I would make the experience point cost for items from Freak Legion at roughly the point cost listed in that book times 100. I figured this would give the players the chance to tweak their characters towards what mutations would best fit their concept but at a price which would hopefully still keep the game in balance.
So please let me know what you think, whether it be advice, tweaks or even criticism of the idea. The more information the merrier as I value the advice of those more experienced than myself.