Using it as a pronoun...

[Enchantedwater]

I think "it" is a good and proper pronoun to use.  It implies not only a shifting undefined nature but it adds an element of mystery.

[mdodd]

The T-1000 was referred to as it in Terminator 2.

[arianne]

Thanks for all the feedback

I just wanted to make sure that "it" was an "okay" pronoun to use.

Mostly I find that when the shapeshifter is male or when the main ("I") character doesn't know him that well, I can use "it" without even thinking, but when the shapeshifter puts on a female face, I sometimes type "she" or "her" without knowing it. Putting "it" onto a "girl" character just feels odd somehow  (Well, no one ever said writing would be logical...)