The Ontological Argument for the Existence of God

[Angrboda]

I'm not schooled in modal systems, I just google S5 and it isn't playing well with the eggnogg I just had.   But I am curious to know what would it say (not my being a little tipsy at the moment) of non-metaphysical possibilities? For example, I don't think it can be ruled out that on another planet somewhere there could have evolved some type of non-metaphysical pink unicorn (pink horse with a narwal-like horn). If it's possible, and the idea isn't metaphysical, then is it necessarily true?

EDIT: Keeping in mind the universe is finite!

The universe being finite is an important question in relation to the ontology of possible worlds and modal logic. As intimated, I'm not a modal realist, so the question of the limits of this universe are relevant. Plantinga however isn't dealing from the same deck. Chad seems to think that a unicorn can't be a necessary unicorn, metaphysically speaking. I think that drags a whole host of questions about the nature of defining God as necessary along behind it, and those questions suggest that a maximally excellent being may not be necessary in similar veins. So I think it's a toss up; if God can be analytically defined as necessary, then there's nothing standing in the way of the same move in the case of a unicorn.