3.Y is a supplement for the d20 System that tries to adapt the game to support old school playstyles. The major changes are: Ability score generation is random, new multi-class rules, the soulknife prestige class becomes a regular class, Concentration is changed to make interrupting spells easier, Diplomacy stops automatically turning enemies into friends, spell save DCs do not escalate, characters can move and make a full attack, and XP is gained only from spending gold.