Can someone explain mantling for me?
Hmm, this may be the best way to explain it in layman's terms.
It's akin to an actor acting out his/her role so role, the character they play as become the actor, in addition to the actor becoming the character. The character and the actor seem so alike, no one can tell the difference between the two. Tiber Septim did this in relation to Shezarr and became Talos.