[Endoperez]

#magicboost <path> <boost>
Gives a boost or reduction to the monsters magic
ability for one or all magic paths. The boost can
be from -5 to 5 levels.

I don't know if you can give a single monster several negative magicboosts, but I think it's possible. If you can't, you could still do it by using -1 or -2 'boost' and giving the mage one or two extra levels in his single path. Unless it's Nature or Death, I think Ritual of Rebirth is the only way you can transform into a shape without negative magicboost. Ritual of Rebirth giving +2 to a single path of magic would be nice, but you can't exactly build a strategy around having your best mages die.