If Stockfish 8.0 is not mercyless enough, please welcome a recent development version ported to Android by Aprijal Pasaribu.
Prior to uploading, i've tested the arm8 build on MTK6752 octa core cpu: 2140 knps in 60 seconds is not a record compared to previous AP builds but it proves at least the compile is healthy. So, it should be the closest engine to perfect chess at present.
I hear you mentioning Cfish?
Ok, ok... In fact Cfish is Stockfish too. It's in the queue thanks to Aprijal.
GET Stockfish dev't 2016.12.03 for 32-bit arm7 pie
GET Stockfish dev't 2016.12.03 for 64-bit arm8
In case of trouble downloading from box, refer to THIS POST.