Mentor spirits aren't much good to adepts. To rectify this I've created adept versions of the mentor spirits in SR4. When a magician or mystic adept chooses a mentor spirit, he uses the mentor spirits as printed in the basic book. When an adept chooses a mentor spirit, he uses the aspect of that spirit listed below.

Adept powers granted by mentor spirits do not count against the adept's power points, but do count against the Magic attribute cap. Thusly, a Cat adept with Magic 4 gains Improved Infiltration Ability 2 at no power point cost, but may only add a maximum of two more levels by spending power points before reaching his maximum of four levels.

Note that the advantages and disadvantages of adept mentor spirits are identical to their counterparts in SR4, except as noted below.

Bear
Advantages: Berzerk.

Cat
Advantages: Improved Gymnastics Ability 2, Improved Infiltration Ability 2.

Dark King
Advantages: +2 dice Assensing, Enhanced Perception 2.

Dog
Advantages: Enhanced Perception 2, Improved Intimidation Ability 2.

Dragonslayer
Advantages: Improved Strength 1, Improved Ability 2 for tests with one social skill of choice.

Eagle
Advantages: Enhanced Perception 2, Piercing Senses 2.

Firebringer
Advantages: Improved Instruction Ability 2, Rapid Healing 2.
Disadvantages: -2 dice to resist Illusion spells.

Moon Maiden
Advantages: Improved Negotiation Ability 2, Kinesics 1.
Disadvantages: -1 Body.

Mountain
Advantages: Mystic Armor 2.

Rat
Same as for magicians.

Raven
Advantages: Improved Con Ability 2, Magic Sense.

Sea
Advantages: Improved Swimming Ability 2, Killing Hands, Water Elemental Strike.

Seductress
Advantages: Improved Con Ability 2, Kinesics 1.

Shark
Advantages: Berzerk, Improved Swimming Ability 2.

Snake
Advantages: Enhanced Perception 2, Improved Reaction 1.
Disadvantages: -1 Body.

Thunderbird
Advantages: Killing Hands, Electrical Elemental Strike.

Trickster
Advantages: Improved Con Ability 2, Kinesics 1.

Wise Warrior
Advantages: Improved Ability 2 for combat skill of choice, Improved Intuition 1.

Wolf
Advantages: Improved Running Ability 2, Critical Strike 2.

Neat ideas, though I'd be more inclined to give skill bonuses than Adept Powers.

Clay

In my opinion way to powerful for 5BP. And most don't even have disadvantages.

I think they are too powerful, but then so too are some of the mage mentor spirits, which can provide half a dozen (or more with a straight skill boost to something like Counterspelling/Binding) skill specialization equivalents for 5 bp and a disadvantage. Admittedly most characters won't be using their bonus spell/spirit dice for Ritual Spellcasting or Banishing, but they're still inclusive boosts.

It was pointed out to me that pure adepts can´t buy the mentor spirit quality (see mentor-spirit quality).

Game-mechanics-wise I´d prefer skill boni, but would balance the 5 build point + disadvantage against a full point of predefined powers if pressed. Imp. ability would only be usable by those who fulfill the requirements of course.

Keep in mind that Mentors also come with a roleplaying requirement, and if the player doesn't adhere to it, they lose the mentor's advantages and possibly even Magic. That's a disadvantage all Mentors have.

And yes, Jaid is right: use the SR4 mentor spirit stats, but where they are contradicted by these, use these.

Ryu:

The Quality itself mentions only Magicians and Mystic Adepts. But:

"Members of any tradition may have mentor spirits, including adepts." Pg. 192, SR4.

A reasonable check on this would be to compare the amount of BP you gain/lose per spirit as a mage against what you gain/lose as an adept.

I'll try to do so later on.

Feel free to adjust them. But what's most sound is the idea of having a version of the mentor spirits suited to adepts.