Minecraft wiki entry for Development_versions, associated text: Fixed an issue where mobs would sometimes render with incorrect geometry when viewed from the Structure Block preview window (MCPE-95183)
Experimental Features: Wither can now be spawned on negative heights (MCPE-125270)
Ghasts no longer spawn in less than 5x4x5 area (MCPE-133687)
Magma Cubes no longer spawn in less than 3x3x2 area (MCPE-46540)
Medium Magma Cubes now have a larger hitbox (MCPE-132159)
Shulker boxes now remain in Dispensers when dispensed at world limit (MCPE-130085)