i think it might be bran straight up
not even warged into someone elses head.
several times he's warged in the past...people have heard or noticed him
when he went back in the past and saw his pops with lyanna....ned stuttered cause he heard him
when he warged in the past into hodors head...hodor looking bran in the eyes before it happened
not to mention the night king seeing him a few times.
im thinking bran went all the way before everything happened before the first men and the children started beefing....and got stuck there. the children of the forest captured him and used him to stop the first men....here enters a paradox
bran exists in multiple places and times all at the same time