Final Fantasy VI Randomizer

"and some of the dragons"?

What do you mean?
Which ones ones of the dragons make you have some problem due to using possess and why?

Well, if you use it on the Holy Dragon, or the Ice Dragon, you'd still have bosses to fight afterwards with only three party members, if you didn't want to exit/return. Using it on the Blue Dragon would result in you having to exit the Ancient Cave without your forth party member, thanks to Warp being unavailable there. There would be a couple other bosses that fall into similar categories too, like Tritoch and the Dream Stooges.