My things : 1. Hair and eyes(and other human characteristics carrying over) 2. Humiliation from the TF(and the humiliation after the TF too) 3. TF involving mammals, especially livestock(I dislike reptiles, fishes, insects and avians.) 4. Most importantly, the overall theme being 'fairytale' like(involving victims being princesses), and 'magical' TFs(poof TFs are okay by me), not science(if it can be avoided). It's because although I love TFs, I draw the line between TFs and real life, and I find the idea of TFs happening in our everyday world quite frightening(and against human rights), akin to a horror novel. Especially if the TF method is 'scientific'. It also almost always leads to downer ending, with the TF being permanent. I prefer 'fairytale' 'magical' and 'medieval' TFs because with magic involved, it leaves some hopes for the reversal and the happy ending(I LOVE happy endings and hopes). Also it is evident that the story is 'fantasy', so the TF is free from human rights issues. I'm writing this because someone had asked me quite a similar question back in DA('what is your opinion on medieval TFs?' which I took to mean 'Why you keep on drawing princess tfs?') which I didn't managed to answer, and seeing this question brought up memories of it
