Crobat ex and Weezing don't go together, only Dark Crobat and Weezing. However your method, you need to do 10 damage to the Pokemon after you use Liability.
As for Dark Crobat, any Pokemon with an attack based on Special Conditions is nice, you're not going to get much more out of it though. Its hard to use just to improve an attack though. I'd go with Weezing or not at all.
TA Kyogre and Sharpedo are really the only options that come to mind. Illumise and Volbeat do a whopping 40 damage for 2 energies if you're afftected by a condition so there's no point in going down that road.
If you can get D. Crobat set up quickly, you can stop Jirachi, Ludicolo, Magcargo, etc. and that's where the meat of the power lies. You're not going to do any real damage but if you can Reversal up a Magcargo and poison it, it will give you a decided advantage.