For a Kylo Ren voice, try our Space Villain Voice Changer app on Google Play (android). This is not real-time though - and the UI is pretty bad. We will try to get a real-time version working also. In the meantime, comments on the voice quality are welcome.
EDIT:
We have added voice changers to our audio recorder app on Android - they can be found under Effects (button on left side) - Voice Changer.
These can be used to make the voice of:
Kylo Ren
Darth Vader
Bane of TDKR
Results will depend on your voice acting as well.
For Bane try with a "vocal fry" type of voice, and inflect like Tom Hardy.
This is the app on Google Play:
https://play.google.com/store/apps/details?id=com.stereomatch.mp3.audio.recorder
The app is an audio recorder - but since it outputs to earphones as well, it can be used for real-time cosplay situations. The app has been tested for 100 hours recording time, and 34 hours on single charge on a Note 4 - so recording should not be a problem.
The app can be used with screen off, and recording can be controlled with 3 clicks of the Power button as well. It has a whole bunch of other features for audio recording - but here I will just focus on it's utility for Cosplay.
LATENCY ISSUE
The problem for Cosplay is that on Android (unlike iOS/iPhone, or hardware devices) there is a considerable delay or latency. This is improving with each Android version, but it is still there - and it can vary across devices.
You will only notice this latency if you are outputting to speakers and can hear them as well. Then even a slight delay will confuse the speaker. You can speak in bursts, but it is still an issue.
To try the app, plug in external speakers, or earphones, and then press Record. Your voice will be echoed on the speakers.
If anyone has any ideas to reduce the latency effect on Cosplay performance, please let me know.
It may be possible to do something like actually increasing the latency so the delay is so large (perhaps half a second) that your own voice is no longer confusing.