Originally posted by Switchblade_Honey:
My suggestion is basically the same system, except that the mutagen kicks in automatically when combat starts.
The reason I think that's better is that the player has probably already mapped the easy-to-reach keys to the core functions. So reaching for the bullet-time key is going to be non-intuitive - if something really bad comes round the corner, you will end up fumbling the key or hesitating and getting killed.
That bit after you hack the ID barrier, when a grunt comes right round the corner - it would have been nice to have a bit of mutagen kick in.
See, problem with that would be annoyence. I don't want mutagen kicking in ever time just one enemy pops around the corner. That and it would annoy the hell out of players that don't even need it. And putting a check box for auto-mutagen would be redundent because it would get so annoying that you'd be forced to turn it off, especially in areas where its not that big a struggle. So in the end, if you do store it up it would be best to use a key stroke rather than a system judging worthyness of use of mutagen which might be more valuable later on.