Having mobility
Has to mean doing less damage
or there is no reason to pick immobile champions.
R.I.P. 
8 Comments
*Doing less damage or having less utility
all of those champions have major utility and arent meant to do tons of damage otherwise they would be broken
It can be any drawback. Lower damage, lower defense, lower utility, etc. As long as the drawback is large enough to keep them from being op, which it isn't in a lot of current cases and most of the immobile champions are somewhat weak now.