I think you are both right here. I think there is just calcualtion server side if winning is possible at all and if not - mod will not help. At the same time winning certain battle may be possible due to pure luck, crit dmg, manual running for skills or even positions on the field. So I think mod works only as long as mathematically winning certain stage is possible according to the server and if not - we receive error. What is quite strage for me is that sometimes I get error with mod, I am turning it off and with some luck I am passing the stage, so that part gets me little confused :) For campain I know for sure that mod works if winning the stage does not give you gems, if there are gems then it usually does not work at all (I guess they implemented additional securities for those).