seedling problems...with the two leafs after the cotyledons

one of them is black/burnt at the tip or shriveled at the tip or something...

might have burn them with your lights, could be heat issues, could be moisture, could be over watering, could be a whole bunch of things. You need to add more info. Growing medium, lights, light schedule, temps, humidity, pot size, what water are you using, whats your PH, have you added any nutes? any pictures?

sometimes they mutate and its natural, sometimes the leaves get stuck inside the shell.

are there ferts in the soil your using? have you fed the plant?