A banishment spell enables the caster to force some extraplanar creature out of the
caster’s home plane. The effect is instantaneous, and the subject cannot come back
without some special summoning or means of egress from its own plane to the one
from which it was banished. Up to 2 Hit Dice or levels of creature per caster
level can be banished.

The caster must both name the type of creature(s) to be sent away and give its
name and title as well, if any. In any event, the creature’s magic resistance
must be overcome for the spell to be effective.

The material components of the spell are substances harmful, hateful, or
opposed to the nature of the subject(s) of the spell. For every such substance
included in the casting, the subject creature(s) loses 5% from its magic resistance
and suffers a -2 penalty to its saving throw vs. spell. For example, if iron,
holy water, sunstone, and a sprig of rosemary were used in casting a banishment
upon a being that hates those things, its saving throw versus the spell would
be made with a -8 penalty (four substances times the factor of -2). Special
items, such as hair from the tail of a ki-rin or couatl feathers, could also be
added to change the factor to -3 or -4 per item. In contrast, a titan’s hair or
mistletoe blessed by a druid might lower the factor to -1 with respect to the
same creature. If the subject creature successfully rolls its saving throw vs.
spell, the caster is stung by a backlash of energy, suffers 2d6 points of damage,
and is stunned for one round.