you will get a dog tag "reborn" cell skins for scar and the other gun cant remember its name. Everything will be reset you wont be any stronger. Its just there if ur bored and want to get everything up again... U also get special achivement unlocks for reboot... like 500 headshot kills with each weapon and each achi gives like 10k xp. Oh and you also get shevron on your rank icon so you can distinct yourself from other non rebooted lvl 50s... the more u reboot the more shevrons u get up to max 5? i think