depends on diet, there is no rebound weight as to speak when you use clen/eca, if you diet is in excess of cals you will add weight, if not you wont. water weight may differ while using something.
when you have done a contest you want to get bodyfat back up to a normal level, its not healthy to keep it too low imo. again once the comp is over most increase there cals to what they would normally take and weight can increase.
imo you are not experienced enough to be using dnp, i think it should only be used by very experienced BB's/pros even then its not a good idea. people have died using 400mg a day, why they did i cant say but you need to know your 100% health wise before using it. i think for someone who just wants to lose a weight faster when they have time to do it a better way its a no,no!