Minecraft wiki entry for Wither, associated text: When spawned, the wither grows larger in size as its health bar fills up. While in this state, the wither is invulnerable, and neither moves nor attacks. When this state ends (after 10 seconds), the wither creates a large explosion centered on itself, destroying nearby blocks and dealing up to 99 × 49.5 damage to nearby mobs/players. This explosion has a blast power of 7, more than that of a charged creeper or an end crystal. It is accompanied by a loud gruesome sound that can be heard equally from across the map and in all dimensions‌[JE only]. After this, the wither attacks nearby mobs and can take damage.