Raid difficulty is a setting that determines the difficulty of the encounters. The options vary depending on the raid, but there is usually a Normal mode and a Heroic mode for each size. It is controlled by the raid leader.
Warlords of Draenor introduced Mythic mode 20-man raids, which are even harder than Heroic. Since then, all raids have been available in Mythic difficulty. Warlords also extended flexible raid sizes to all non-mythic difficulties, including Raid Finder. This leaves Mythic difficulty as the only fixed size of raid.
In Mists of Pandaria Patch 5.4, Siege of Orgrimmar introduced the Flexible Raid mode that scales in difficulty depending on the number of players from 10 to 25. Drops are better than Raid Finder, but worse than 10-man Normal mode.
- All raids introduced before Patch 3.2.0 will use 10-player Normal mode for the former normal mode (10 man raids) or 25-player Normal mode for the the former heroic mode (25 man raids). Burning Crusade raids likewise only have fixed 10-man or 25-man sizes.
- All newer raids beginning with the Crusaders' Coliseum can use the 10-player heroic mode and 25-player heroic mode settings to access harder versions of the raids, not to be confused with hard mode actions/events within the same raids.
- Blizzard has greatly added to the complexity of raids by changing the composition of modes with almost every expansion.
- Patch 7.0.3 (19-Jul-2016): Variations on Mythic mode based on .
- Patch 6.0.1 (24-Apr-2014): Flexible Raid mode was effectively replaced by a flexible Raid Finder mode.
- Patch 5.4.0 (10-Sep-2013): New Flexible Raid mode for Siege of Orgrimmar.
- Patch 3.2.0 (04-Aug-2009): Introduced.
Prior to Patch 3.2.0 you had to use the Dungeon difficulty setting.