I had an answer until I reread and saw 'reptile'. (I worked with some exotic arachnids that were a pain to keep- specifically Galeodes granti or the Egyptian Banded Solifugid (you might know them as a sun or camel spider). But as for reptiles...I've only kept corn snakes and bearded dragons. I did have a boa for a while- I guess she was the most difficult but not horribly. I'd like to try a GTP but have heard they are difficult.