Once you have unlocked a persona, it can be selected in the Player Status menu. This image will be your avatar in duels.

Persona	How to unlock
Persona 01	Mulligan down to one card and then win the game.
Persona 02	Attack an opponent with a copy of a creature.
Persona 03	Counter a spell that's targeting a spell you control.
Persona 04	Exile a creature.
Persona 05	Deal 10 damage that's not combat damage to a player in a turn.
Persona 06	Cast five spells in a single turn.
Persona 07	Gain 20 life during combat in a single duel.
Persona 08	Have twenty or more lands on the battlefield.
Persona 09	Deal 10 combat damage to a player with flying creatures in a single turn.
Persona 10	Win during an opponent's combat phase.
Persona 11	Play an online match between midnight and 1:00 a.m. local console time.
Persona 12	Win a duel while at 1 life.
Persona 13	Viral Unlock
Persona 14	Have a life total of 100 or higher.