Well, like any strategy that involves changing abilities, you have to keep both Pokemon alive for it to be actually useful. And that also means you have to use Plusle or Minun and keep them alive long enough to use Entrainment and have its partner be able to take advantage of the effects of Plus or Minus, which is highly unlikely given the pair's atrocious bulk and only middling Speed.
FATECRASHERS MADE MY AVATAR! Go look at more art!
Currently out, college apps are poison. C&Cers, contact me if you need any help with anything important. Sorry!