Boss Mobs

As seen by a Forum Post, boss mobs will be introduced.

Rarity
When a hostile mob spawns, it will have a 1 out of 75 chance to become a boss mob.

Drops
Boss Mobs drop the drops of whatever mob they are, aswell as having a high chance to drop a Special Chest, which will contain much rarer items than your standard Treasure Chest.

Appearance
When a boss mob is spawned, they will have red particles swirling around them, or some other particle effect that can be easily noticed.

Mobs versus Boss Mobs
Boss Mobs will contain a speed effect, as intended to insure the effect that if you're in combat with a Boss Mob, you're not getting out (Although the /visit command might be as of effect). They are much, much stronger than your average mob, aswell as having a lot more health than your average mob.

Holiday-Based Boss Mobs
As hinted by Incomprehendable, Holiday Based boss mobs may be added on holidays. Killer Snowmen have been hinted to be added, aswell, so on holidays, beware!