Is immune to Silence and builds resistance to Sleep quickly(first Sleep II may stick without Elemental Seal, however subsequent attempts at sleeping will more than likely require ES). Other status effects, including Stun, seem to have a normal chance for landing.
Seems to be resistant to Repose, WHM could not land with capped Divine Magic despite two attempts.
Fairly succeptible to Head Butt as long as it's not spammed, repeated use will make him resist the stun, but if you lay off for a short while, the resistance seems to recede.
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.
His storm spells decrease the damage done by Elemental Magic of the same element. For example, Thunderstorm decreases damage done by Thunder based spells.