Correction, below y:0 no hostile mobs spawn and unable to spawn wither.
Iron golem and snow golem spawn with no issue down to y:-59, haven't tested further, will update if I do.
Matthew Wolfenden
Correction, below y:0 no hostile mobs spawn and unable to spawn wither.
Iron golem and snow golem spawn with no issue down to y:-59, haven't tested further, will update if I do.