Rare monsters are powerful monsters in Diablo III, being direct descendants of the Diablo II Unique monsters. They can be distinguished from other monsters by their yellow glow and yellow name. They have more health and hit harder than normal monsters, but have a higher chance to drop loot when they are killed. Rare monsters also have many minions which are not as strong as the rare monster, but are much stronger than their normal counterparts. Two affixes only appear on rare monsters: Horde and Missile Dampening.
Note that minions do not have to be of the same (or even similar) monster type as the Rare monster itself. This can lead to situations in which minions prove even more dangerous than their leader. However, for a confirmed kill (getting the reward), players do not need to kill all minions, killing the leader is enough.
Minions are always linked to their Rare leader with AI. If character hits one of them, the entire group will try to attack the player, unless blocked by impassable terrain.