Sunny's plan was rather simple. Since the mental protection granted by the Undying Chain was not enough to break through the mind hex of the unknown horror, he just had to get better defenses.
Of course, he could have summoned Saint, who was completely immune to that kind of attack. If he had no choice but to fight the abomination, which Sunny suspected to be a Corrupted Terror, he would do exactly that… but at this point, he was simply trying to understand what exactly was happening, and how.
Considering that Saint would not be able to communicate what she saw, he had to try breaking through the hex himself, first.
