Question about Possession-based Traditions, and Mentor Spirit Modifiers. Options

[milk ducks]

I'm a little confused on how this stuff in Street Magic works, maybe you guys can help?

Let's say I follow the Voodoo Tradition (Possession-based), so Combat is handled by Spirits of Man. In Possession-based Traditions, a spirit's Materialization power is replaced with Possession, and when they use it against specially-prepared vessels, they have to make opposed tests to see how successful the merge was. Okay, so let's also say that the summoner (and in this case, the vessel) has taken the Dark King Mentor Spirit, which gives him +2 dice for Spirits of Man; does the Summoner get this dice bonus in the opposed test, or does the Spirit of Man gain the bonus against the Summoner? I guess it's not altogether clear to me.

Also, I'm not sure how to get a spirit out of your own body once it's in. It says, "The spirit is under no obligation to return to its metaplane of origin if/when its services are banished away and will simply persist as an uncontrolled spirit indefinitely." Maybe I'm missing something?

-milk.