I did some searches and couldn't find a thread about this question.

If a mage of a possession tradition makes an ally spirit can it have both Materialization and Possession?

On page 103 of Street Magic under step 2: Choose Forms it says the spirit may have either Materialization or Inhabitation.

On page 104 of Street Magic under step 3: Choose Powers It says the extra powers for force are "chosen from any powers available to spirits the initiate may conjure"

Since Possession is a power available to spirits of his tradition, the mage takes it as one of the force powers.

I cant find anywhere in street magic that explicitly says Materialization and Possession are mutually exclusive.

There is a posibility for a spirit having both as per the listing under Free Spirits' new powers on page 107 of Street Magic. It lists Materialization and Possession together (literally) under the powers available and doesn't say anything about a single spirit not being able to have both.

This is covered in the Errata. Possession tradition mages can select Possession or Inhabitation, but not Materialization.

A single spirit cannot have both, and Materialization mages can never have Possession Allies.

However, a Possession mage can effectively have Materialization Allies, by picking a vessel and skewing the roll so that an Inhabitation Merge has no chance of resulting in anything but a True Form.

It means that the spirit will tend to take on a Materialized form looking like whatever the vessel looked like.

So, if you want a human-looking Ally, Inhabit a mannequin.

Or a hobo.

Or buy a cloned body (25,000 from Augmentation), get all the desired Cosmetic Surgery you dark heart desires....

Yes, but in that case (spending real cash), you'll probably be aiming for a successful Inhabitation, rather than a Materialization (see: CyberAlly).

Also, don't forget... sustained Physical Mask or shapeshifting spells.

and of course, you'll have to dikote him . . her . . IT!

That's a given.