Within X-Men universe have there been cases where an individual unintentionally died because of technicalities of their powers?
X can fly, but
X doesn't know he can only fly in total 1 hour per day (suppose between 00:00 day 1 and 00:00 day 2). Eventually,
X flies really high, after 1 hour his power disappears (as he's used used up his power for that day),
X plummets down and dies.
Y can shoot water balls that explode. When
Y is near a water source (suppose near means within a fixed radius), that source is used to create the water balls. At some point,
Y uses his powers not within a water source and his body explodes as
Y did not know that some liquid was required to feed his power.
Note: mutants that eventually figure out the technicalities or side-effects of their powers through usage do not count.