In The Binding of Isaac, there is Guppy's Head, which can help you become guppy. Theres also Tammy's Head and Max's Head. In Rebirth, will there be more Max/Tammy items, and if so, will you be able to become Max/Tammy?

not enough tammy items to become a tammy.. and max items will turn into cricket items (one of our other cats, i never had a dog named max).

but there should be a few new “final forms” that you can become by collecting X number of set items.