Asking for assistance on tumblr is quite unhelpful so I'm tossing this over here where I hope sometime somehow we can uncover more Klonoa media. I understand some of these are total shots in the dark... but stranger things have happened. I think it's important to at least bring attention to these and more.

This is gonna be image heavy.
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More sprite rips! (The most image heavy, beware.)
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Also a bit image heavy...
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Clearer shots/scans of Klonoa merchandise. There's a lot of merchandise in the tag on Klonoa @ Blog but sometimes the pictures we find are small/low quality/not scanned. Also, any magazine scans we currently don't have is welcome!
Merchandise tag for reference:
https://klonoa-at-blog.tumblr.com/tagged/merchandiseSpoiler
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Two guidebooks were published for the game Namco X Capcom. Klonoa characters appear in this game. Of interest is any artwork or pages inside these books relating to the characters. Apparently, there are storyboards for the intro animation in one of these books which Klonoa makes a brief appearance in as well.
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熱血野球 !! ファミスタ (Literally: Hot Blooded Baseball!! Family Stadium) is a comic published in Comic Bun Bun magazine by Hitoshi Ogino to promote Family Stadium DS 2009 for the Nintendo DS. Klonoa, along with other Namco characters, appear as baseball players. Currently, the full comic hasn't been found. There are multiple chapters and only a few panels are floating about the net.
Found so far:
https://klonoa-at-blog.tumblr.com/post/185772658183/%E7%86%B1%E8%A1%80%E9%87%8E%E7%90%83-%E3%83%95%E3%82%A1%E3%83%9F%E3%82%B9%E3%82%BF-literally-hot-blooded-baseballhttps://klonoa-at-blog.tumblr.com/post/179898074200/%E7%86%B1%E8%A1%80%E9%87%8E%E7%90%83-%E3%83%95%E3%82%A1%E3%83%9F%E3%82%B9%E3%82%BF-literally-hot-blooded-baseballSpoiler
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In Ridge Racer 6, there's a track called Aviator Loop that has two Klonoa billboards. While this track also appears in Ridge Racer 7, the Klonoa billboards are not present. We would love clearer screenshots of them or textures from the game.
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Been curious about what Klonoa is doing in this guidebook for World Stadium 3(?) but scans of it would be neat.
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Klonoa was one of the opponents in Namco's Seven Bridge card game as part of their App Carrot (アプリキャロット) service for older Japanese cellphones.
It is likely to remain lost media like all of Namco's old cellphone games.
Video:
https://klonoa-at-blog.tumblr.com/post/184447030786/klonoa-at-blog-footage-of-the-old-klonoa-mascotFootage of the old Klonoa mascot costume performing an on-stage dance. This is assumed to be at the World Hobby Fair in 2002 when they were showing off Klonoa Beach Volleyball. The original source of this footage is unknown and the audio is missing. I believe they're dancing to Stepping Wind? We got photos and one or two instances of short footage for Klonoa hanging around booths at shows, but more would be awesome but it's probably vanished from the web or nobody has such a thing around.
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An old magazine published in Japan called 日経CG (Nikkei CG) showcasing computer graphics and technology had a story about the making of Klonoa: Door to Phantomile's intro animation. The exact issue is No.138, March 1998. A .pdf of this is available online but it is only accessible to students of the Nara Institute of Science and Technology. We may have already seen bits of this from Hideo Yoshizawa when he was discussing the intro storyboards in his Klonoa Chronicles tweets.
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There's so much lost/missing Klonoa media, it's dizzying. If anybody can help or think of more, throw it here. Maybe someday a master detective can help us find it all. Until then, here it is in one place.