Allen is a young man of average height with medium-length whiteish hair and silver eyes. Allen has an unusual scar on the left side of his face that starts as a pentagram on his forehead and trails down his face through his eye. The scar is the source of his Pentacle Eye, which allows him to see human souls. His left arm, from his shoulder down, is red and veinous, and can turn into a huge claw weapon.
Allen is a very depressed character who used to be fairly enthusiastic. He is somewhat timid and has grown into a wise but pained character.
In season four, Allen was sometimes considered the main character. He was the most popular worker at the Pokemon Daycare. He was later recruited for the new daycare.