You may get a message stating, "The hands of darkness prevent you from proceeding," after being checked to enter the battle. Originally thought to be held back due to a campaign battle, but entry was allowed shortly after still during the battle.
Is immune to Silence and Resists Sleep (BLM was able to land Sleep II first time without ES; 2nd and 3rd times required ES..) Other status effects, including Stun, seem to have a normal chance for landing.
At 50% HP, he will use Tabula Rasa. While under its effect, his Stratagems do not wear off, allowing him to cast spells under the simultaneous effect of all of his Stratagems.
At around 15% HP, he gives up and the battle ends.