o.o you can't save on mobile , these data saved with webstorage (like cookies on browsers) so it will be saved there , he want to tell you if the game is having waves every wave getting more harder than the older one you should use global variable but if not waves use sprite.variables
for example you have sprite called ship and has (8 frames = 8 kinds of ships) and you made sprite variables so now you have variables like this (speed attack,speed move,hurt,life,...)
so in event sheet you will do this:
condition:sprite:compare frame = 0
action: put speedmove = 10 , put lifes = 2, put hurt = 1 , put.....
condition:sprite:compare frame = 1
action: put speedmove = 50, .....
and so on in all frames so in this way you just put ships and they will have thier own powers they will not get stronger anymore (this way for no waves games)