Raids: 10 & 25 man raid scale starts from 5 for 10, 10 for 25
and continue to scale per person, example 20 players would scale as 20 players
and full groups for Raids/dungeons will be as they are normally.
Raids before ICC 25+/RS are soloable scaled
(The Burning Crusade and Classic Raids are also scaled down)
Trial of the Crusader Hc: 2+ for 10 Player, 3+ for 25 Player
Icecrown Citadel: 1+ for 10 Player, 5+ for 25 Player
Icecrown Citadel Heroic: 5+ for 10 Player, 10+ for 25 Player
Ruby Sanctum: 1+ for 10 Player, 6+ for 25 Player
Ruby Sanctum Heroic: 6+ for 10 Player, 10+ for 25 Player
VOA ICC Toravon Boss: 1+ for 10 Player, 10+ for 25 Player
Raids before ICC 25+/RS are solo soloable scaled
Some bosses are designed for more than 1 player so you will still need another player in some cases and some classes will be better than others at solo content.
These raids scale lower per person than the end game raids in order for all classes to do them.
(with exception of some bosses - we don't want to be a full solo server!)
Eye of Eternity
Ulduar (Exception Yogg-Saron/Thorim, not solo 2 bosses)
Vault of Archavon (Exception ICC Toravon 25man, not a solo boss)
ICC 10 man normal only
RS 10 man normal only
Scale from 1 to 5 Players
Timed dungeons with rewards and require 5 players (based on mythic dungeons on retail)
Another good way to farm current tier items!
Check the mythic vendor in-game