I can run bluestacks emulator fine, but for some games which require dodging, it would be easier if I had more time to think. That said, is there a feature that allows me to explicitly reduce the fps or make it slow motion?
Probably not, or if it was "slower" it would be "laggy" and have poor input performance, i.e. touch a button but takes to long to respond, or have jerky rendering performance.
Games are typically designed with a minimum performance requirement so they can run the physics and graphics engines for their content. The games are play tested at a standard frame rate (most likely 30 or 60 fps on Android) and would only have "easy modes" like "slow-mo" or "bullet time" modes if designed from the start.
If the game developer used an existing third-party engine with standard input, there may be settings which can change touch lag performance externally but basically would mean hacking the game.
While there are various articles online on how to make Bluestacks NOT lag and you could do the inverse, I doubt it would be fun experience. Reaction time games are just that, reaction time games. Given that most are designed by a younger generation, all I can suggest is to provide feedback to those developers to provide some accessibility options which may/may not make sense for any particular game.