The Lost Skull is a common mob added by the Mo' Withers mod. They have 5 types: Skeleton skull, Wither skeleton skull, Creeper skull, Player skull and Zombie skull.
Spawning[]
Lost skulls spawn uncommonly, about 5 times as rare as the Wither Cultist, in the Overworld in packs of 2 to 4. They also spawn commonly in packs of 4 in the Nether. When naturally spawned in the Nether, they have a 1 in 5 chance to become a skeleton skull, and otherwise a wither skeleton skull. When naturally spawned in the Overworld, they randomly choose a skull between the 5 types.
Description[]
Lost skulls are 0.5 block tall (0.6 block tall for wither skeleton skulls) cubes that take the appearance of their corresponding mob head. Their hurt and death sounds are the same as that of the corresponding mob.
Behavior[]
Wither skeleton skulls are immune to fire, while the others does not. Skeleton and zombie skulls will burn in areas with a light level of 8 or more in daytime. All skulls emit smoke particles around them.
When attacking a mob, the skull will inflict 4 seconds of Wither I if it is a wither skeleton skull, but all skulls has a 1 in 5 chance of setting the mob's attack target to nothing. All skulls will attack twice per second when they are within 7 blocks of their enemy's center, except for creeper skulls, which explode itself with a power of 2. Lost skull attacks does 2 damage.
Lost skulls will chase their target if they are within 32 blocks. They will continuously accelerate to their target.
Strategies[]
A single hit with an iron sword or better will be enough. Skeleton, zombie and player skulls don't do much damage, so they can be easily destroyed. Wither skeleton skulls will inflict the wither effect, but a quick hit with an iron sword or better before they have the chance to hit you will do. Creeper skulls are the most dangerous, but you can survive them with good armor. Shooting lost skulls with a bow is difficult, because their small size and their fast speed.
Gallery[]

Many Lost Skulls of all types in a bedrock room.

Lost Skulls attacking cows.