Pressure plates where the wither spawns/falls? Can't remember if there are warded/otherwise wither proof versions of those...
Waiiitttt. Arcane ear. Can that thing be set to the wither noises, or even explosions?
I think it can only attuned to noteblocks, sadly not really to anything it "hears" player/mob-wise.
But I will test a new way, over night I had the idea of maybe working with "Detect if netherstar was collected by hopperhock" to make the golems only activate after the Wither is dead.
Sometimes ideas come right before falling asleep xD
[edit]
*sigh* Had a good working system planned out... just to notice that the use-core for Golems seems useless on a server (cause of no mob-griefing or so x.x).
Anyone knows another way, with the mods of this modpack, to autoplace a wither into the world?
I heard about some mechanic with witchery but no idea about it. (and if it's worth the effort, since the server only allows to place withers in the nether... so don't want to build a whole witchery-altar-setup there. Besides automating and protecting it from getting destroyed seems really difficult with how the rituals work)