Yu-Gi-Oh! Duel Monsters ALEX (lost unreleased Japanese version of anime series; existence unconfirmed; 2006)
Yu-Gi-Oh! Duel Monsters ALEX, known as Yu-Gi-Oh! Capsule Monsters outside of Japan, is a 12-episode anime spinoff of Kazuki Takahashi's Yu-Gi-Oh! manga franchise. Produced as a way to promote a Mattel toyline loosely based off of one of the games featured in the manga, the miniseries was a US-Japan co-production between 4Kids Entertainment, Nihon Ad Systems, Studio Gallop, TV Tokyo and Shueisha. The series premiered in western markets on television and as two 90-minute direct-to-video movies in 2006. 
To date, Yu-Gi-Oh! Duel Monsters ALEX remains the only entry in the franchise to not be released in Japan. The prior co-production, Yu-Gi-Oh! The Movie: The Pyramid of Light, was released in the country as a TV film. It's been theorized that the spinoff has been denied a domestic release due to it not being in the same continuity as the main series. The same reason is believed to have kept Toei's 1998 Yu-Gi-Oh! anime from being re-released.
It's not actually known if the series has a Japanese version, though Studio Gallop lists the production under a Japanese-specific name. Katsumi Ono, director on this series and various other Yu-Gi-Oh! spinoffs, has expressed interest in seeing the show released in Japan.
- Yu-Gi-Oh! Singaporean dub - The second Yu-Gi-Oh! series received a little-seen English dub produced in Singapore.
- Yu-Gi-Oh! Zexal - The third Yu-Gi-Oh! spinoff series received an unreleased English dub produced in Los Angeles.
- MATTEL PLANS COLLECTIBLE FIGURE GAME Retrieved 03 May '17
- Yu-Gi-Oh Capsule Monsters DVD in May Retrieved 03 May '17
- Yu-Gi-Oh Movie to Stream Online Retrieved 03 May '17
- 4KidsTV Fall Lineup Retrieved 03 May '17
- Ask John: Why Hasn’t Yu-Gi-Oh! Capsule Monsters have Been Released in Japan? Retrieved 03 May '17
- ぎゃろっぷ作品履歴2009 Retrieved 03 May '17
- 誰か遊戯王ALEX編の日本語版を出そうと企画出す人はいないものか・・・ 「デュエルアーマー・シルエット！！」て日本語で聞きたいぞ。 Retrieved 03 May '17