Yuugo "Hugo, Pawn of Fusion"
About
Despite his short temper and rudeness, Yugo is a kind person at heart, especially towards Rin, his childhood friend, whom he has feelings for. He himself is also aware of his short temper and apologizes immediately once he realizes it upsets someone.
He is the Synchro Dimensional counterpart of Yuya Sakaki (Standard Dimension), Yuuto (Xyz Dimension), and Yuuri (Fusion Dimension).
Yugo displays on occasion the strange ability to Synchronize with his dimensional counterparts when he is dueling. In this state, Yugo and his counterpart's personalities are mixed together, causing both parties to adopt some mannerisms of the other, including speaking the same words and moving in the same manner.
(Source: Yu-Gi-Oh! Wikia, edited)