Summary of the problem Lag during wither fight Pack Version 3.0.15 What is the bug? When I am fighting the Wither, the mob just freezes and does not react to any hit with the sword, then it unfreezes and fires a wither ball that gives the poison effect. This repeats and repeats until I die. The Wither effect takes almost 30 seconds to wash away, making this fight very frustrating and time consuming, and there is no item in the pack to resist against the effect except the brew of absolution which is too hard to craft, requiring all sorts of ingredients I can't remember. TheJ JEI recipe is too long to find out, requiring me to skim through all the potions. The Wither fight should work or at least the modpack should not require any Nether star to go through. The only mod requiring Nether stars is Draconic Evolution which I'm willing to skip as the fusion crafting is too repetitive and time consuming, but the RFTools dimension builder was modified to require Awakened draconinium, which is why I'm now blocked by Nether star. Mod & Version Draconic Evolution RFTools Dimensions Probably the modtweaker allowing to alter recipes Link to log file Is it repeatable? Spawn a Wither boss inside a cage of Reinforced glass Known Fix After a lot of tries, it ends up working, but this is very painful. The only workaround is to automate killing of the Wither, but the only block I know of that allows this is the Mob Grinder, which itself requires Awakened Draconium. Having a crafting recipe for Nether stars would greatly help.