What qualifies as mainstream?

mainstream is basically a franchise (movies/cartoons/games/comics/books/magazine) that the common folks and common reader knows about. Whether you're a longtime reader, a hardcore reader, a casual reader or a nonreader, chances are that you will be familiar with Batman, Superman, Spider-Man, X-Men, Hulk and Iron Man.

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-Gohan vs Mujin Buu-
Buu: So hot shot, you want to fight Mujin Buu?

Gohan: Fight you? No, I want to kill you.

Well the common reader would know about almost all of the ones you suggested so I was a bit confused.

Well, not everyone. Many ppl don't know Lupin III, and ppl still don't there's a "The Mask" comic around.

Try to find one thats underground. But still kind-of big!

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-Gohan vs Mujin Buu-
Buu: So hot shot, you want to fight Mujin Buu?

Gohan: Fight you? No, I want to kill you.

I like popbot

In that case I would guess Usagi Yojimbo would be on my list of non-mainstream according to your definition.

I heard of that Comic before. Mostly seen it on TMNT. But yea, I heard a lot of good stuff out of it.

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-Gohan vs Mujin Buu-
Buu: So hot shot, you want to fight Mujin Buu?

Gohan: Fight you? No, I want to kill you.

Gyakashu by Dann Hipp, published by Tokyopop
Last Call by Vasilis Lolos, published by Oni Press
Black Metal by Chuck BB and Rick Spears, published by Oni Press
Aqualeung by Paul Maybury and Mark Andrew Smith, published by Image
Scott Pilgrim by Bryan Lee OMaley, published by Oni Press
King City by Brandon Graham, published originally by Tokyopop, now being published by Image
Umbrella Academy by Gerard Way and Gabriel Ba, published by Image Comics

Ｓｏｒｒｙ　ａｂｏｕｔ　ｔｈｅ　ｗｅｉｒｄ　ｆｏｎｔ，　ｃａｎ＇ｔ　ｇｅｔ　ｒｉｄｅ　ｏｆ　ｉｔ：

mainstream is basically a franchise (movies/cartoons/games/comics/books/magazine) that the common folks and common reader knows about.
Ｉ　ｄｏｎ＇ｔ　ｓｅｅ　ｈｏｗ　ｙｏｕ　ｃａｎ　ｃａｌｌ　Ｈｅｌｌｂｏｙ　ｎｏｎ－ｍａｉｎｓｔｒｅａｍ．　Ｉｔ　ｈａｓ　ＴＷＯ　ｍｏｖｉｅｓ．ＴＭＮＴ　ａｎｄ　ｔｈｅ　Ｍａｓｋ　ｗｅｒｅ　ｂｏｔｈ　ＨＵＧＥ franchises in my childhood. And Lupin is a pretty classic anime/manga series. Hell, when I was reding Hellblazers people kept asking me what it's about. The conversations all went like this:
"It's about a dude name John Constan---"
"OMGＣＯＮＳＴＡＮＴＩＮＥ？！　Ｉ　ｓａｗ　ｔｈａｔ　ｍｏｖｉｅ！＂
＂．．ｏｈ．．．ｙｅａｈ　Ｉ　ｔｈｉｎｋ　ｔｈｅｒｅ　ｗａｓ　ａ　ｍｏｖｉｅ　ａ　ｗｈｉｌｅ　ｂａｃｋ，　Ｉ　ｗａｓ　ｔｏｏ　ｙｏｕｎｇ　ｔｏ　ｗａｔｃｈ　ｉｔ．＂

According to your definition I have to pick the Best-selling comic book ever. The Sandman, because it still doesn't have a movie yet (although it has a few spin offs only hardcore fans care about)

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