Power Levels, Character sheet, and all you need to know

phases per stage being Early, Mid, Peak

Low-class devil/angel/ 2 wings fallen angel/Low-level demons(mindless)

Mid-class devil/angel/ 4 wings fallen angel/Mid-level demons(basic speech)

high-class devil/angel/ 6 wings fallen angel/High-level demons(Can fluently speak)

Ultimate-class devil/angel/ 8 wings fallen angel/Humanoid Demons(Can transform into a human)

Satan-class devil/angel/cadre-level fallen angel/low-level Gods/Demonic Generals(Demons that are highly intelligent and powerful)

Mid Level Gods/Demonic Commander(same as demonic general but they have Devil Trigger)

High level Gods/Mundus

Heavenly Dragons/Urizen/DMC 5 Vergil

Ophis/Great Red(Baka red)

Reincarnated Demons Power level

phases per stage being Early, Mid, Peak

Low-level demon(Improved vitality)

Mid-level demon(Improved stats)

High-level demon(Devil trigger or summoning their Persona)

Ultimate-Class(Persona 2nd stage or awakening)

Tbh I don't like using power levels, 'for me' those levels are the amount of energy you can dish out. Issei can even fight a High-class devil while being a low-level one himself. It all depends on your combat strength, combat experience, and your trump cards.

Character sheet:

Vergil Redgrave

Mayumi Saegusa (Mahouka Koukou no Rettoussei)

Summons:

Griffon(Crow/bird familiar)

Pantera(Panther familiar)

Groc(Golem familiar)

Suicune(Pokemon) [https://www.google.com/amp/s/pokemondb.net/amp/pokedex/suicune]

Silvers Rayleigh(One Piece) [https://www.google.com/amp/s/www.pinterest.com/amp/pin/363806476125013116/]

Francis Scott Key Fitzgerald(Bungou Stray dogs)[https://www.pinterest.ph/amp/pin/24347654215891464/]

Louisa May Alcott(Bungou Stray Dogs)[https://www.google.com/amp/s/www.pinterest.com/amp/pin/805651820817183493/]

Sui Feng/Soi fon(Bleach)[https://www.wallpaperflare.com/bleach-soi-fon-1200x1774-anime-bleach-hd-art-wallpaper-qoapz]

Saeko Busujima(H.O.T.D.) [https://funnyjunk.com/funny_pictures/1532912/Saeko/]

Hildegarde/Hilda(Beelzebub) [https://www.zerochan.net/762466]

Saiba Jouichiro (Food wars) [https://aminoapps.com/c/anime/page/item/saiba-joichiro/X1tX_IgoaK0vDK13DDVKVBQ3MQV4Nk#media-562c2a30]

Milluki Zoldyck(HxH) [https://aminoapps.com/c/anime/page/item/milluki-zoldyck/QDtY_I3Dej5G7pJz8vgWb6roPp801B#media-b25e2b17]

In case you don't know the differences of the difficulty gamewise:

Human: For chilly inexperienced players and just wants to watch the cutscenes and played for the story only.

Devil Hunter: For those who want a 'little' bit more spice in the game.

Son of Sparda: In this mode, enemies tend to deal more damage, and can have higher health. This is usually unlocked after beating the game once. This is the game's equivalent of Hard Mode.

Dante must Die: In this mode, enemies are tougher, have twice the amount of health, and use more attacks. In past games, enemies gain a Devil Trigger which they can use against you.

Heaven or Hell: For those who wants more spice in their plates; In Heaven Or Hell mode, players can die in one attack, however, enemies can also die in one attack.

Hell or Hell(For the masochistic Bastards): In Hell And Hell mode, players also die in one attack, and are given 3 lives. However, enemies do not die in one attack, and is similar in behavior as that of Dante Must Die difficulty