The other form is the Right Edge, the sword of exorcism. It’s used to draw the evil out and will not harm innocent people. His arm becomes a massive sword which he pulls free of his body, it is capable of the Cross grave still but it has a few newer attacks. He can create a shock wave slash of sorts. The cloak still makes up for some of his now smaller range, but this is the powerhouse form. Not much else is known about it.
Two other things Allen is able to do. He can control the Ark of Noah using Timcampi as his sheet music, its believed he’s the requirement of the player. And then there is the cursed eye that can see the souls within Akuma, its evolved once and can peer about him with a limit of 300 yards.
Background: *WARNING, SPOILER HEAVY* (If you need this more detailed I can redo it.) Allen was found by Mana Walker after being abandoned by his birth parents because of a deformity. Mana took him in and raised him till he passed away. After his foster father passed on, Allen was lost in grief and turmoil. The Earl offered to bring his loved one back, Allen accepted. If not for the innocence imbedded in his deformed hand like everyone else who agreed, he’d have been killed. Instead he was cursed by Mana and destroyed the man who had raised him releasing his soul from the imprisonment of an Akuma body. General Marian Cross found him and once the boy accepted began to train him to be an exorcist. For three years he traveled with the man and learned from him.
Afterwards Cross ditched him so Allen had to make his way to the Black Order on his own. After a misunderstanding with Kanda Yuu, Allen was officially declared an exorcist. It wasn't long after this he was sent on his first mission. As time went on he was sent on his second mission; there he met a new accommodator (Miranda) and encountered one of the Noah (Road). During his recovery after the battle, he met Lavi the apprentice Bookman. Komui assigned them to the long term mission of finding General Cross and before they could get underway Allen was held back.
The side trek this caused lead them to Krory another accommodator of innocence who had been misunderstood. On the train to catch up with the others, Allen met Tyki Mikk who he didn't know was another of the Noah. It isn't mentioned how long it took, but we next see Allen in China hot on Cross' trail. Anita, Cross' latest lover points them towards Japan. However before they could set sail, Akuma seem to attack but they're actually after something else, the Fallen exorcist Suman Dark. Allen tries to save him, but between being one of the Fall and being an incubator for Tease? It was far too late and Tyki strikes while Allen is down.
He recovered Tyki's assassination attempt and Bak the section chief of the Asian branch tell him his innocence isn't destroyed. It takes Allen until a true battle with an Akuma strikes to invoke. He quickly headed off right after to Edo to help the others. His arrival had perfect timing, turning the tide of the battle before they are all swept into the Ark. In a race against time Allen and the others battle their way through each room that is being downloaded into the new Ark. When the few who kept going reach the top, Allen battled Tyki though the tide of their battle shifted twice.
When it seemed all was lost Cross at last showed up and dealt with things swiftly. With a precious few minutes remaining before the download was complete, the general has Allen reverse it. With the Ark and all its contents as a prize of victory, they returned home. Despite being put under suspicion by the Vactican, Allen rushed off to help when the science lab was attacked. Sadly even though the generals and other exorcists also fought, several of the research team lost their lives. The Egg had to be destroyed thanks to Lulubell taking Miranda hostage. But its not over, an Akuma evolved to level four.