Originally Posted by Light
I +10 both my myth kingdom guardian, but one broke going for +11, so I didn't risk it anymore.
one assumption is that item name colour makes a difference, however Red is the "most common breaking" but it didn't break getting both to +10, so that throws that assumption away.
Well..the other reason that it wouldn't break that fast is because kingdom guardian of myth or normal equip is level 50+, low level requirement compared to other common items (bonus/myth equips).
Red = unstable type of item but the item name colour is just rarity though, which you already sort of implied Light.
But yea, I find that I can +7 my forgotten snow girl set items easily compared to my other items..and as for grading myth equips, they do have extreme properties compared to normal equips.