Dark Soul

A Dark Soul is a NetNavi's soul engulfed by a Dark Chip's influence. Generally, the Navis body turns a blackish purple.

MegaMan Battle Network 4
MegaMan uses a dark chip as the only way to defeat ShadeMan. Throughout the game, MegaMan is faced with the temptation of using the power of Dark Chips, but is able to suppress his dark soul enough to keep under control.

Later in the game, it is discovered that Chaud used a Dark Chip on ProtoMan as a last ditch effort to delete 500 evil Navis. ProtoMan's Dark Soul however, had taken over him over and he became evil, detaching himself from Chaud. MegaMan chases ProtoMan into the Undernet and confronts him. Under the operation of Chaud, MegaMan is able to defeat and capture ProtoMan DS and his dark soul is suppressed.

At the game's climax, MegaMan is forced to confront his Dark Soul in battle before fighting Duo. MegaMan's Dark Soul's fighting style is very much developed based on MegaMan's and has the same HP and Navi Customizer parts equipped. MegaMan defeats his Dark Soul and then continues on to defeat Duo.

MegaMan Battle Network 5
MegaMan gets kidnapped by Nebula forces and receives a "Dark Chip implant" turning him into Dark MegaMan. Nebula places him in charge of controlling End Area 3 and only returns to normal after being defeated by the liberation team. Also, in Nebula Area 6, DS versions of friendly Navis in the game can exist independently from the original NetNavi's body.

MegaMan NT Warrior
In the anime, Navis using Dark Chips will start to develop blotches of black or purple on its body. It should be noted that this is only shown happening to FlashMan and DesertMan. Also, MegaMan turns dark after a painful bite to the neck from ShadeMan.

Dark Soul Navi
A DS Navi (Dark Soul Navi) is a NetNavi who has been corrupted by the energy of a Dark Chip. DS Navis first appeared in MegaMan Battle Network 4 along side the introduction of Dark Chips. In both Battle Network 4 and 5, all NetNavis that the player can battle in the game have a DS version of them, even Bass (Bass XX). A DS Navis' HP and attack strength are determined by MegaMan's DarkSoul Level, and is 1% of MegaMan's base HP (or the first number). The number isn't rounded.

Difference between Darkloids
A DS Navi can become normal after the Dark Chips's effects wear off, but Darkloids use Dark Chips as their primary source of life and power.

Especially, only three Dark Souls can evolve into Darkloids and exist on their own: Dark MegaMan.EXE, Dark ProtoMan.EXE and Dark Colonel.EXE.

Battle Chips
When a DS Navi is defeated (or when achieving the specific busting level against an SP Navi), MegaMan will receive that Navi's DS Chip. DS chips, like Evil Chips, can only be used by dark NetNavis. The power of these DS Navi chips also depends on MegaMan's DarkSoul Level. In MegaMan Battle Network 5, MegaMan can't use these chips if he isn't in Dark Mode (gained by using Dark Chips before), but other Navis (only in Liberation Missions) can use them. 