Is TR a problem for you? I can see how Rotom-W can be a problem. It has great typing, offensive capabilities, and bulkiness. The thing with TR is that it relies on its heavy hitters since they have a limited number of turns to be effective. if you have something that can cripple and/or wall their threats then the match should be in your favor. Also, stalling TR is a viable option. Fake Out, Taunt, Protect/Detect are all moves to take into consideration. Also, pokemon that can utilize priority moves are excellent against TR teams because the still get to move first, even if they are not slow.
On random MU i just pick my team selectively and play my smartest against others. I try to predict what they will bring in against me and the moves i think they run on their team. My current record as of now is 61-40. Ive been on a bit of a loosing streak lately =/. sorry for the hasty response. if you want more detail just ask =)