Raid Bosses are very powerful creatures that are typically invulnerable until some arena mechanic is activated. They are also often supported by hordes of weaker creatures.

When you create a Raid Boss encounter, consider the Mechanic behind making the Raid Boss vulnerable to damage. The mechanic can be as simple or as complex as you would like. For a simple example, an Elite creature could spawn amongst the swarms, which drops a special object on death. You then take that object and use it to somehow break the Raid Boss’ invulnerability.

The Stat Blocks provided here are examples of Raid Bosses.

(NOTE: Though these are called "Raid Bosses") you may also use them as lesser boss encounters, as they have Mechanics like any other.