I saw a few comments about what skills Allen has and which ones will be in the future.
Allen had a dream where Neah D. Campbell or Walker the fourteenth Noah appeared.
so his abilities when he's become a Noah
Noah's skills: Allen Being a Noah can call the ark with his thoughts and teleport wherever he wants through the doors are inside the ark itself.
previously I had said his "features" of Noah, could materialize and dematerialize as he wants, similar to Tiky's ability, why that ability and not another? easy: according to D. Gray man's manga, which is still ongoing, many secrets aren't known about Neah when he was from the Noah Family, only that he killed all his brothers and sisters in that period. so since this is a Fan-fiction, and I found that ability useful, so I added it.
As I said, Allen before he came to the world of "Highschool DxD" he had already traveled to other worlds, which later if my dear readers want to read about his "past" I will write them.
One piece:
Three types of Haki:
Allen has all three types of Haki on a higher level than a Yonkö, so he can exercise his will to other people and if he wants to, he can kill them.
Kokutö Yoru:
the sword of his old master, Dracule Mihawk, where he received him and gave his knowledge about being a noble swordsman despite being a pirate.
Spoiler Alert: Mihawk passed away and in his last breath he gave him his sword to follow in his footsteps. and be the best swordsman in the world. which achievement in the world of One piece.
Seirei Tsukai No Blade Dance:
the world of spirits where Est and Restia come from.
Est and Restia both have swords which have been their companions for years.
Allen also has the 'Absolute Blade Arts' which were taught by the old witch Greyworth Ciel Mais.
Spoiler Alert: he first got Est (as in the novel Kamito got it, Restia had no owner at that time, but later in a tournament his carrier was discovered that was already corrupted by the elemental king of darkness, what did what a Heaven child or a protagonist would do, eliminate evil, blah, blah, blah.)
Restia was about to be eliminated by the corruption but Allen saved her and gave her another chance as her second spirit hired and finally liberating the corruption of the other elemental kings.
SPOILER ALERT: READ UNDER YOUR OWN PRECAUTION.
Fate / Stay Night
As the title says, Allen can create a Reality Marble where his "inner world" is full of swords stuck in the ground, while the ground is reddish and the sky a crimson sunset like blood.
Allen has the mythical skill called UNLIMITED BLADE WORKS. Why does he own it and not Shirou Emiya as he should?
I have previously commented, Allen has traveled to alternative worlds, which is why he will not always follow the "cannon" of the worlds, or history.
it is supposed this skill Allen still does not handle it well, although he knows many noble Phantasm, but he will occupy it later against Kokabiel in the ark of the Excalibur swords. which will cause him pain because he remembers a certain gluttonous girl who always had a strand standing in her blond hair.
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Before forgetting, remember Allen has a curse of immortality. for which reason he can not die for any reason, only to be eliminated with Hakai-type powers, which will not appear in this novel. so please do not compare him to a fried chicken which was brutally traumatized in the chapters.
for now those are his abilities and worlds which he traveled. It's up to you if later on after the young devils tournament Allen reveals his past to the girls who are in love with him.