I don't usually have nightmares that are obviously related to being trans, but usually when i think about them i realize they're related to dysphoria. sometimes i dream that i look like a boy, but everyone else sees a girl, and they think i'm crazy when i point out that my body is a boy's body.
when i was thirteen though, i had a horrible nightmare that stuck with me. I was riding a bike and i ended up in hell basically. i don't think i knew how i got there, but i was riding through a dark grey/ black area with sort of a path ahead of me. on either side there were horrible demons doing horrible things, and though they never pulled me in, i didn't know if they would. i kept riding my bike, and there were sort of ramps, and i kept trying to ride real fast up them so i could get up out of where i was, but i just kept doing a back flip on my bike, never quite making it out, and riding down the path until i reached the next one. my brother was above, and he was trying to help me out when i was flying off the ramps, but he couldn't reach me. so, i just kept cycling through hell. looking back on it, i'm pretty sure it was about menstruation and puberty in general.
other than that, i just have generic tornado, sometimes monsoon, dreams a lot. they seem to be my default nightmare.