Unknown how the selection of spells they'll cast is determined.
They will not attack unless attacked. When attacked, he'll draw his hammer and start attacking the aggressor. This will often happen in battles with monsters that use AoE attacks (such as Battle Dance).
Has a finite MP pool, as of such will actually be seen in the Command/heal stance to recover MP and HP. You will often see them /heal after all Campaign mobs nearby are defeated and Campaign still continues because another wave is on the way.
In the event that the unit they arrived with retreats, they will remain on the battlefield and not retreat, remaining to assist anyone nearby and to fight if attacked.
Have low defence and HP compared to other units, as of such they wont last long when attacked.