Here is the guide lines.
Both of you bring up good points. Ok here lets lay some for sure rules and guild lines.
Playable Characters:
Dante/Sparda (Whether he is a costume or the real him we'll all figure out later)
Vergil
Nero
Trish
Lucia
Lady
Credo (secret player)
Mundus (secret player) (Why not? He'll have a human like size)
Cameo appearances:
Patty Lowell (DMC Anime girl)
Kyrie
Matier
Enzio
Veiwful Joe (A poster or picture of him, or him himself)
Setting:
Fortuna city
Limbo City (That's where Dante's business is located at in the DMC1,2,3,4,anime right? Or does it have another name)
Temen-ni-gru
Dumary Island
Mallet Island (Maybe)
The demon world
Weapons:
Rebellion (All of Dante's weapons from DMC1,2,3,and 4)
Yamato (All of Vergil's weapons from DMC3SE)
Red Queen (All Nero's weapons from DMC4)
Trish (All her weapons from DMC2)
Lucia (All her weapons from DMC2)
Lady (All her waeapons from DMC3)
Credo (All his weapons from DMC4)
Mundus (All his powers from DMC)
Weapns created by us, when thought of.
Enemies and bosses:
All enemies and bosses from DMC1,2,3,4, and anime can be used.
Story line: Takes place after DMC2, and we can also include a prequel element for Nero like Meg brought up.
Those will be the guide lines, let's work around this.