A banishment spell is a more powerful version of the dismissal spell. It enables the character to force extraplanar creatures out of the character's home plane. Up to 2 HD of creatures per caster level can be banished. To target a creature, the character must present at least one object or substance that it hates, fears, or otherwise opposes. For each such object or substance, the character gains +1 on the character's caster level check to overcome the target's SR (if any) and +2 on the saving throw DC.
At the DM's option, certain rare items might work twice as well (each providing +2 against SR and +4 on the spell's DC).