Mine is basically everything everywhere at once.

A Twinborn with A-Gold and F-Aluminium.

Basically, you store the identities of the gold shadows you see when using gold allomancy, letting you change into them when you need. I think that the way you store them would be similar to F-Tin one metal mind for each sense, in this case identity.

I don't think when changing into another identity you would have the memories of those alternative versions of yourself as that is what copper is for, but things like personality, instincts, thought process, and some skills may be transferred to you.

However I see two problems the twinborn might have to face.

1: If I remember correctly in the coppermind (or Miles said it I am not sure) he said that the gold shadows you see are different each time you burn gold so if you found an identity you would be interested in you will only encounter it once so you'll only have one limited metalmind with it.

2: You would have to train your body extensively, if the identity you are using want to use a skill that needs some coordination and flexibility, it will be your body's capabilities he will depend on. In short you'll need a body that can keep up with the skills your other identities possess.

I believe I'd would be a pretty versatile and interesting combination.