Drops

Rare drops are items dropped by killed monsters, which occur especially infrequently and in addition to the regular drops. Unlike regular drops, they only occur if the monster is killed by a player, similar to Experience Orbs. All rare drops can also be obtained by other means.

Rare drops have a 2.5% chance of occurring when a monster dies, and a 20% chance of being enchanted rare drops. Using a weapon with the Looting enchantment increases the chance of a rare drop by 0.5% per level, and also increases the chance of enchanted weapons (up to 50% with Looting III). All types of non-enchanted rare drops are equally likely.

Enchantment is chosen the same way as one from Enchantment Table with a cost of 5 levels. This means it is possible to get multiple enchantments.

History
Rare drops were first added in Minecraft 1.2.