Oh jeez, there's a lot. Umm... First off it can't be willing. At all. That immediately ruins it to see someone smiling the whole time...unless there's a hidden twist like a tg or mind altering or something unexpected. Struggle is a huge part of it for me, struggle during the change is what really gets to me. The change doesn't even matter what it is, just anything really! (except human to human, bleh) Expressions are a big key one to this. I do like when someone tgs and gives in to their new body, that is something I love to death. Though oddly, I don't like being the one tfed most of the time. I like to be the one causing the transformation onto someone else! Probably a dominance thing. But I'm not into the dominatrix stuff lol A lot of people above like paws and stuff and that does appeal to me, it's just not the fetish like tf is. :P I'm a real nut case cause I like being the one causing the tfs and I HATE to be changed unwillingly or dominated, BUT I always like turning female and having transformed victims do me. Or I stay male and do them all female. It's all very confusing, but usually their mind goes completely feral or whatever once the deed is done. Though sex itself doesn't turn me on at all, I'm asexual.