None. A summoned spirit has a damage threshold equal to its summoner's heal value; any attack which deals more damage than that threshold banishes it back to the spirit world until re-summoned, while any attack which deals less damage is ignored. When a spirit you control is banished, you take psychic damage equal to your heal value.
6. The spirit ignores difficult and treacherous terrain.
Armor: 16 + half caster's level.
Reflex: 10 + half caster's level.
Fortitude: 16 + half caster's level.
Will: 10 + half caster's level.
You may command the spirit to perform a Bear's Maul as a Rank 1 trance, using your Skill and ability modifiers.