Well, I'm tired of all the misinformation about Lord of Chaos, so I decided to make a page explaining it.
Lord of Chaos is a secret boss fightable in exe5 after you beat the game once. Upon reavhing NebulaArea 6, you will find 6 doors. They are unlocked by either beating or S-ranking each of the Team SP Omega Navis.
Once they are open, there are spirit things inside. Talking to them will cause encounters with the DS team navis.
The time in which you beat all the DS Team Navis combined decides what you face next. Move to the dark gate in the center of the area. It should be gone now, allowing you to pass through.
Going up the stairs, you reach a NebulaHole. Approaching it triggers a cutscene in which Lord of Chaos appears. The form he takes depends on the time you beat the DS navis in, but the first time he will ALWAYS he NebulaGrey;
0-1 Minutes - NebulaGrey
1-2 Minutes - RockmanDS
2-3 Minutes - Forte(Yes, I said Forte. The people who say he's only fightable with Forte-Cross-Rockman are either lying or very misinformed).
Also, if you beat him as Forte, ForteSP becomes a random encounter in NebulaArea6.
Now here are the encounter scripts, when a name is said in text, I replace it with the Japanese name but leave the NA name in ()s;

The NebulaGrey form that's always first -

Rock: The DarkPower's coming from here...
Netto: Keep your eyes open...
Rock: Gotcha...
Rock: ...Yikes!!!
Netto: What is it, Rockman(MegaMan)!
Rock: Something's coming out of the Vortex!
???: GHAAAAAAH
???: I AM THE CHAOSLORD.
???: I HAVE COME TO RULE THIS CHAOTIC WORLD...
Rock: His DarkPower is incredibly strong...
Rock: Here he comes, Netto(Lan)!!!
*screen flashes and NebulaGrey appears*
???: NO MERCY FOR THE PURE OF HEART...
Rock: Here he comes, Netto(Lan)!!!
Netto: Ok, Battle Routine Set!!!
Rock: Execute!!!
*fight with a 2500 HP NebulaGrey called "ChaosL(o)rd" starts*
*Rock pwns him(In my case with his own chip!)*
*the NebulaGrey begins to delete*
???: OHHHHHHHHHH...
???: I HAVE COME TO RULE THIS WORLD OF CHAOS...
???: ...I SHALL ENDURE AS LONG AS THERE IS DARKPOWER...
*the NebulaGrey deletes spectacularly*
Rock: That was some power...
???: One gigantic evil reation has faded..
Rock: Wh-who's there?!
*Rock looks around*
???: A great evil still lurks on this planet...
???: You must fight until evil is vanquished...
*chipdata falls*
Rock: ...A BattleChip?
Rock: I-it's...
Game: Rockman(MegaMan) got a BattleChip for "BigHook G"!!!
???: Evil will again return one day...
???: The only way to defeat it is to keep fighting....
Rock: Who the...?!
???: I am the one who conquers evil...
???: I am always watching... Farewell...
Rock: Hey, wait!
Rock: ...It's gone.
Rock: The one who conquers evil? Who's that?!
Netto: Don't sweat it...
Netto: It's just one of those things....
Netto: Let's head home.
Netto: We still have a lot of things to do.
Rock: ...You're right.


LoC as Forte;

Rock: Netto(Lan), that's from power emanating from that vortex...
Netto: What'll come out...?
Rock: I'm gonna be crushed by this pressure!
Rock: Here it comes!!!
*screen flashes*
???: ...Battle against me.
*Forte stands outside of the vortex*
Rock: ...!!
Forte: I must taste this power that has awakened me...
Rock: Netto(Lan)!!!
Netto: There's no way out!
Netto: Battle Routine, set!
Rock: Execute!
Forte: This shall be fun...
*a battle starts against a 3000HP Forte with the name "ChaosLrd"*
*When you win, you get a busting level for once, and I think no matter what level it is, you get "Forte(Bass) F" (Or ForteAnother in ToC)*
*Rock wins*
Forte: So you've got the power to counteract evil...
Forte: I must get the power of absolute evil.
*Forte retreats into the vortex*
Rock: He's gone...
Netto: That was some power...
Rock: Yeah, one false move and we'd have been toast...
Netto: We gotta keep getting stronger...
Netto: Strong enough to beat any evil...
Rock: I can get stronger because of you Netto(Lan)...
Rock: Strong enbough to beat any old evil!
Netto: Got that right!


LoC as DS Rock;

Rock: Uh-Uuh!!!
Netto: What is it Rockman(MegaMan)?!
Rock: I feel terrible!
Rock: I feel this cruddy sensation welling up in my soul...
Netto: Hang in there!!!
Rock: Aaaaaaaaah!!!
*screen flashes*
*RockDS stands in front of the Vortex*
Rock: Is this...is this me?
Rock: I get it! Ti's the darkness in my soul!
Rock: Here it comes Netto(Lan)!!!
Netto: Rockman(Megaman), you must conquer the darkness in your soul!!!
Netto: Battle routine, set!
Rock: Execute!!!
*a battle with a 2000HP RockDS called "ChaosLord" begins*
*Rock wins(and once again, I used the LoC chip, it was the weakest of the three by far)*
*the screen flashes and RockDS vanishes*
Netto: Is's...it's gone?Rock: It's back inside me.
Netto: We can't defeat it?
Rock: As long as we have a soul, evil will endure.
Rock: But after that last battle, I'm confident I can beat it!
Netto: It's like they say: We're all our own worst enemy.
Netto: But I know we can battle the evil within us!!!
Rock: Right!!!
(No reward is given after this fight)


LoC as NebulaGrey the roulette version;

???: GRAAAAAAH...
???: NO MERCY FOR THAT WHICH NEGATES EVIL...
Rock: Something's coming!
*screen flashes and NebulaGrey appears*
???: I SHALL KEEP RISING AGAIN AND AGAIN...
Rock: Here he comes Netto(Lan)!!!
Netto: We'll keep knocking him down!!!
Netto: Battle routine, set!
Rock: Execute!!!
*a battle starts with a 3000hp NebulaGrey called ChaosLrd*
*Rock wins(Once again, I won with the LoC chip)*
???: RAWRRRRRRRR...!!!
*The NebulaGrey deletes spectacularly*
Rock: We did it somehow...
Rock: I wonder if he'll rise up again...
Netto: If he does, we can handle him, right?
Rock: But of course!!!
Rock: As long it's you and me Netto(Lan), we can beat anybody!
Netto: That's right!
(Again, no reward)