You know, about some of the cameo characters...
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like Ripot and Plum, it's a little weird to think that advanced robots like them existed before Dr. Light completed the first 8 robot masters. But then again, it's not like the games ever said exactly when they were made.
Oh yeah, and I've been copying and pasting this cameo list around message boards. Let everyone know if you find anything to add!
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The Metall Potton, a great big Met dispenser from Mega Man 6, appears in Wily's laboratory. Another one appeared in Mega Man's background stage in Marvel vs Capcom, a stage that was set out to look like a Wily fortress. There are a few other elements on that same page that are similar to that background stage as well, like the caution striping and the image of a skull-shaped battle vehicle being worked on, partially hidden by one of the walls. Other enemies shown in the beginning include the Yellow Devil, Big Eye and Bunby Heli (aka Blader), all of whom appeared in Mega Man 1 (though the Bunby Heli looks like the Mega Man 8/Mega Man & Bass version).
Edited by Sb20 on May 14, 2011 at 15:13:04
In the city view behind Titanium Park, there is a round building where part of the CAPCOM logo is visible. There's a large sign suspended from this building, which at first I thought was the tail end of a Street Fighter IV logo, but it doesn't quite match, so maybe it's something else. This building resembles another building shown in the Mega Man Official Complete Works book on page 43, which had a "Street Figher' V" advertisement on it. The city also contains tube-like highways similar to those in Mega Man 9's opening scenes.
Ripot, Plum, and Chest, three robots who presided over the racing events in the game Mega Man Battle & Chase, are present at Dr. Light's press conference as reporters. Ripot introduces himself as a reporter for the "B&C Gazette".
Another reporter at the conference looks exactly like Neige, a human photojournalist from Mega Man Zero 4.
There's yet another reporter at the conference and who also delivered the Channel 8 TV news report on the robot rampage. She identifies herself as "...Li," probably a reference to Chun Li who appeared as a TV reporter in Mega Man 9.
The Channel 8 logo is based on the Rockman (red triangle) logo! I completely missed that before.
At the press conference, the podium Dr. Light presents from has an image of Dr. Light that resembles his game sprite.
The city's police force are modeled after the Mega Man Legends Kattelox Island police.
Cut Man's shut-down look resembles his appearance on the cover art of the Japanese Playstation version of Rockman 1.
Guts Man's (posterior) is a popular youtube meme, and is displayed in one panel where Dr. Wily is reprogramming the robots.
One of the buildings Cut Man and Bomb Man are shown attacking reads "CAP PLAZA", Plaza Capcom is the name of Capcom's arcade centers in Japan.
There's an image that resembles the Darkstalkers character Huitzil (an ancient alien robot) on a container of nuts and bolts.
The operating table Rock is attached to during his transformation into Mega Man is based on the one that appears in the story segment of Mega Man Soccer.
Some of the equipment shown at Light Labs in the wrecked Lab scenes and the Mega Man reconstruction scenes are based on background details from Mega Man Powered Up, including the large crane arm suspended from the ceiling and the monitor that displays Mega Man's internal schematic (based on the Mega Man cross-section art shown on page 198 of the Mega Man Official Complete Works book).
The exterior of Light Labs is based on how it appears in many of the games, and Dr. Wily's fortress is modeled after how it appears in Mega Man 2.
Dr. Light's pipe and Roll's Powered Up broom appear in the backgrounds of certain scenes.
The Short Circuits strip pokes fun of Bad Box Art Mega Man and the Ruby Spears cartoon's theme, the "Super Fighting Robot" part.
There are some other things that might not be intentional:
Rock's shoe-shine cloth is a long yellow fabric that looks a little like Proto Man's scarf.
Dr. Light's big green furniture with the large bolts sticking out is vaguely reminiscent of Auto.
Thanks to RedJokerZero and Hypershell for contributions to the list!