To make life easier, play on "Very Easy" mode.
Tangram is the final boss of Arcade mode. He is vulnerable when his eye appears. I used Angelan for this. I kept dodging with Y and X and B until the eye showed up. When the eye was there, I used LT once, backed up, I let loose a few hits with RT, dodged once, got halfway to him, and used LT again. Then his eye went away, I dodged some more, it appeared, and I used LT, RT x 2, and LT again from mid range. He was dead.