Alter Aeon Online Help

Keywords are:  'necromancer spell boneprison prison bonecage cage'

Spell: bone prison              Mana:  45  Int: 25  Wis: 23  Lvl 21 Necr  (28%)
                                (helpful)   Requires: bone armor
                                Group: Necromancer Dragontooth Skills

Usage:
cast bone prison <target>

This spell uses a small number of teeth, usually 5-7, to create a bone
prison to trap the target.  The prison does not last long and the target
can usually break out rather quickly, but it can provide enough time
for the caster to flee or recast defensive spells.  Stronger and larger
targets will be able to break out more quickly.

The spell has a fairly high mana cost in addition to requiring teeth.
The large amount of mana is needed to create the prison quickly enough
to trap the target.