Demonic speech effect:

1. Reverse the audio
2. Apply reverb
3. Reverse back again

You may have to realign and ensure that reverb tail is not cut off.

Try also to change the pitch a few steps down without changing tempo.

Demonic speech effect:

1. Reverse the audio
2. Apply reverb (ensure that reverb tail is not cut off)
3. Reverse back again (You may have to realign audio manually)

Try also to change the pitch a few steps down without changing tempo.

Try a tempo alignment / hitpoint detection tool and shuffle the tempo a little to create weird phrase rhythm

You probably should wait with the demonic effect till you applied other tricks, since it will be degraded or make it more difficult for the other effects to work.