I didn't found that bug... one of my friends did (or maybe he found that on another website) and I wanted to share it because I thinks its gonna be fixed anyway.
With this bug you will be able to 1 hit kill anything, all you have to do is to be instant cast ( about 1540 haste ) and you gotta use Hunter's Mark on the boss/player before attacking him with your bow. If you want to be instant you have to get haste items.
Get about 1100 haste and just use a haste potion that give 450 haste then use Hunter's Mark and shoot an arrow and its gonna die 1hit.
if asked by many ppl I'll remove this post XD
Edit: For those who didnt understand... In eternion there are 50M hp bosses... which take alot of time to kill... even if ur are instant cast it take alot of time to kill them... the bugs that I explained above is a 1hit kill bug... it takes only 1 arrow to kill. You gotta shoot an arrow! dont attack him with ur weapon...