So i've decided to see what bossing is viable at 1 defense. Seeing as i couldn't find a guide I thought i'd make a list. Some the following is taken from reddit, will update list with new information as it comes to my attention via comments and input from the community and personal experience, hopefully find some new bosses to hunt in the process as I am not very familiar with pvming.
Chaos fanatic
Range this guy as he has super high melee defense. Protect from magic. He only attacks with mage. Sometimes he shoots out 3 green blobs, just walk away from them and they won't hurt. There's an altar just south west from him so you should restore prayer after every kill. (Or mid kill if you're low prayer and don't use pots)
Crazy Archeologist
Mage this guy because he has super high range defense and he uses melee + range in melee range which would destroy a pure in 3 seconds. He has an attack pretty much identical to chaos fanatic, just avoid the 3 orange blobs he shoots out (and the 2 blobs that explode out of those) There are safespot(s) also I believe you can snare/entangle him.
Callisto
Protect from melee and constantly attack him in melee range. I think godsword is best. He can hit 60 and avoid prayer so always stay as high HP as possible. Best to duo him but solo is doable. Might be hard to do this boss with less than 85 hp level.
Mole
Protect from melee. Poison is useful (dds is good cos he's weak to stab) Bring stamina pots because he runs away and you gotta chase him.
KBD
Probably have to range him cos you can't use hasta and whip is pretty bad on him. So... Just bring antifire pots and an antifire shield, don't even need to pray when ranging cos he only attacks with "Dragonfire" which is NOT magic and armour doesn't help against. So just wear your best range gear and attack him, don't go into melee distance. His def is high so pots and eagle eye flicking is recommended.
Kalphite Queen
Protect from range or magic (Literally doesn't matter which one, they're both 100% accurate and hit same) Use melee when she's protecting from range, use range when she's protecting from melee. Don't stand in melee range when ranging. Remember to bring antipoison.
SCORPIA Mage recommended Trident/Iban + snares, pray range and stay out of melee range. ZULRAH will post when I learn rotations or someone posts summary. GOD WAR BOSSES You can do Bandos and Zammy if you have a tank with another 2-3 ppl. You would only be able to kill Arma and Sara if you have a mass.