Sorry, OP. The task you're going to attempt is impossible. Here's why; Light level is an average of all your attack and defense values of your gear. Khvostov has 5 attack. Assuming your current light level is your highest, if you were to equip the khvostov, you'd be left at 239 light at most. The nightfall is 280, leaving you unable to do damage while being one-shot by everything.