I have two separate accounts and for some reason, when I go to train my pet, one costs 4 energy to play one game, and the other costs 6 energy. They are roughly the same level (47 and 50 respectively), and the lower level one actually costs less to train pets than the higher level one. So I don't think it's based on level. Firstly, what IS it based upon, and secondly, why on Earth does the energy cost vary from one wizard to another? I never noticed it before today, oddly enough, but I thought it had always been 4 per game.
I would appreciate an answer, as I spend a ton of real, actual, US dollars on this game - to the point that I am ashamed to say it - so I expect a swift reply, please. This irritates me no end, and it makes no sense at all.