The Soul Series contains characters who cannot be selectable, they are usually the final bosses of every game, many unselectable characters are proven stronger then selectable characters, some may be even weaker. Unselectable characters could be playable with cheat devices that could nearly crash the game and create glitches. However, not all unselectable characters vary by power or excel, some are just common foes and easy to take down. Inferno is the only non playable character in Soul Calibur II, Soul Calibur III had a bunch, including Night Terror.
Soul Calibur II
Inferno rises once again, about the same but slightly stronger, he changes fighting style when you knock a quarter of his health, playing as him with cheats causes the game to freeze on certain occasions, playing as him makes you play in all stages, as normally, Inferno is only fought in the last stage, Tartarus.
Also, there are 2 characters found only by cheating named "Q. Takagi" & "Wovama." Q. Takagi is basically Cassandra's Player 2 Outfit using Kilik's weapons & fights like Mitsurugi. If used in a fight, Q. Takagi's health bar will show Spawn's name instead no matter what system you used Q. Takagi in. Wovama is basically Cassandra's Player 1 Outfit using Astaroth's weapons & fights like Nightmare. If used in a fight, her health bar will show no name at all where the character's name is supposed to be. It is unknown if they have an ending & what happens when they're in a Destined Battle.
Soul Calibur III
This game has many: Shadow Master, Doppelleganger, Colossus, Will-O'-The-Wisp, 3 forms of Charade (a full version with Wave Sword moves, a blob & legs form with Grieve Edge moves, and a blob which uses Cassandra's horizontal & vertical attacks— the blob cannot throw or be thrown; all 3 forms have a special move that shoots a laser from the eye of the blob) common Lizardmen, and Night Terror. Those characters could be easily playable with cheats. Other unselectable characters could be fought; these are Gladiators and created characters with individual names and different voices (most likely Berserker's voice). The iron swords of the Gladiators do not map properly to the models' hands. The created non-playables have no extra effects on gameplay, they could all be created easily. Unknown Soul is just a darkened character.
If players happen to have an Action Replay Max for the PS2, they could be playable with no glitches, though going to modes like character profile or tales of souls freezes the game. Though the non playable creations could be playable with cheat devices, 1 difference is that the announcement says the name of the character instead of the job name. Unknown Soul and Keres can also be playable with a PAL Action Replay Max only.