Here is an overview of the update, via Square Enix:
In this update, players can embark on–or relive–the adventure of a lifetime with Sora and friends in the all-new Critical Mode, an additional high-difficulty mode that will challenge players in their fight against the darkness.
Critical Mode will challenge even the most skilled Keyblade wielder to be more tactical as they battle formidable foes. In this new mode:
- Maximum HP and MP are halved.
- The frequency of situation commands and magic is lowered.
- Sora can perform new abilities exclusive to this harder difficulty mode.
Additionally, this update adds the feature for players to carry over their Keyblades to a new game. Keyblades that are carried over will return to their default strength, but through this optional feature, players can utilize Keyblades otherwise not obtained until later in the game from the beginning.