Looking through the Mentor Spirits both in the SR4 main book and in Street Magic, nearly all of them give bonuses to one spell type, and one skill. Adepts, however, never get any spells, but are allowed to have a Mentor Spirit. The book does say that GMs and players should feel free to come up with a Mentor Spirit that's more in line with the character's philosophy, but I imagine that the balance may be hard to get right.

Does anyone have such a character in their game? How do you handle Mentor Spirits for Adepts?

Some Mentors give bonus to certain skill tests. These might be good if you really want something in exchange for buying that positive quality.

...I had an adept with the Trickter Mentor. A very good on in that it adds dice to her Con tests. The GM has also let her apply the +2 bonus for illusion spells it to her willpower roll to resist illusions.

i'd probably handle it the same way . . if a totem, ahem, excuse me, MENTOR SPIRIT, choses you as his Pawn, why should he/she/it give you any more power in aspects you simply can not do if it can just chose to give you more power in an aspect you CAN do? i'd probably subtract any pool modifiers for spellcasting either plus and minus and add the remainder on the other aspect that gets a bonus . .