|This article is about a/an episode in Kamen Rider Gaim.|
Rider Great Assembly! Revealing the Mystery of the Forest! (ライダー大集結！森の謎を暴け！ Raidā Daishūketsu! Mori no Nazo o Abake!) is the tenth episode of Kamen Rider Gaim. It features the TV debut of Ryugen Kiwi Arms following its first appearance in Kamen Rider × Kamen Rider Gaim & Wizard: The Fateful Sengoku Movie Battle, as well as the debut of Takatora Kureshima's first on-screen transformation into Kamen Rider Zangetsu.
Kouta and Mitsuzane begin to postulate on the identity of the white Armored Rider who seems to be destroying all evidence of the Inves entering their dimension. To try to figure out what should be done about both the Inves and the white Rider, Kouta decides to consult with the other Armored Riders
Christmas is fast approaching and while doing a part time job, Kouta finds two Inves attacking a woman and rescue her before finishing them. With the increasing incidents involving the Inves, Kouta and Mitsuzane decide to investigate the Helheim Forest to look for clues, but they must beware of the white Armored Rider. Mitch then comes up with an idea, by inviting Kaito, Ryoji and Hideyasu for a game in the forest, with the team catching the most Lockseeds declared as the winner. As Team Gaim is the only team with two Riders, Kouta agrees to sit out of the game, as his true intention is to have the other Riders distracting the white Rider and his minions while he looks for clues about the Inves and Yuya's whereabouts. To give Ryoji and Hideyasu access to the forest, the Riders convince Sid to provide them some Lock Vehicles but he claims that he will have them ready by Christmas. Mai gets angry at Kouta and Mitch for proposing such game just when Team Gaim is on top of the rankings but they calm her down, claiming that it is necessary for them to learn the truth about the Inves and they promise to will return in time for their Christmas party. On the day of the game, the Riders are about to start when Oren appears, convincing them to join after he reveals that he also possesses a Lock Vehicle. However, once several Inves appear before them, Kamen Rider Baron runs ahead of the others to the forest to have an advantage, with Bravo following soon after. To delay Ryugen further, Kurokage and Gridon feed a Himawari Lockseed to an Inves to strengthen it and rush to the forest as well. With all other Riders away, Gaim appears to assist Ryugen who fights the Inves as the new Armored Rider Ryugen Kiwi Arms and instructs him to run after the others. Before leaving, Ryugen lends Gaim the Suika Lockseed to help him dispose of the enemies. Upon knowing of the Riders appearing at the Helheim Forest, Takatora transforms into Armored Rider Zangetsu as he is about to depart there as well.
- Kouta Kazuraba (葛葉 紘汰 Kazuraba Kōta): Gaku Sano (佐野 岳 Sano Gaku)
- Kaito Kumon (駆紋 戒斗 Kumon Kaito): Yutaka Kobayashi (小林 豊 Kobayashi Yutaka)
- Mitsuzane Kureshima (呉島 光実 Kureshima Mitsuzane): Mahiro Takasugi (高杉 真宙 Takasugi Mahiro)
- Mai Takatsukasa (高司 舞 Takatsukasa Mai): Yuumi Shida (志田 友美 Shida Yuumi)
- Takatora Kureshima (呉島 貴虎 Kureshima Takatora): Yuki Kubota (久保田 悠来 Kubota Yūki)
- Chucky (チャッキー Chakkī): KANON
- Rica (リカ Rika): MIINA
- Rat (ラット Ratto): Ren Ozawa (小澤 廉 Ozawa Ren)
- Hideyasu Jonouchi (城之內 秀保 Jyonouchi Hideyasu): Ryō Matsuda (松田 凌 Matsuda Ryō)
- Ryoji Hase (初瀬 亮二 Hase Ryōji): Atsushi Shiramata (白又 敦 Shiramata Atsushi)
- Ryoma Sengoku (戦極 凌馬 Sengoku Ryōma): Tsunenori Aoki (青木 玄徳 Aoki Tsunenori)
- Oren Pierre Alfonzo (凰蓮・ピエール・アルフォンゾ Ōren Piēru Arufonzo): Metal Yoshida (吉田 メタル Yoshida Metaru)
- Lock Dealer Sid (錠前ディーラー シド Jōmae Dīrā Shido): Kazuki Namioka (波岡 一喜 Namioka Kazuki)
- DJ Sagara (DJサガラ Dī Jei Sagara): Tomomitsu Yamaguchi (山口 智充 Yamaguchi Tomomitsu)
- Sengoku Driver Equipment Voice (戦極ドライバー各種アイテム音声 Sengoku Doraibā Kanren Aitemu Onsei): Seiji Hiratoko (平床 政治 Hiratoko Seiji)
- Narration (ナレーション Narēshon): Hōchū Ōtsuka (大塚 芳忠 Ōtsuka Hōchū)
- Mother: Noriko Tanisaka (谷坂 宜子 Tanisaka Noriko)
- Child: Kohei Noguchi (野口 晃平 Noguchi Kōhei)
- Researcher: Shunsuke Innami (印南 俊佑 Innami Shunsuke)
- Lock Used:
- Orange, Suika, Sakura Hurricane
- Banana, Rose Attacker
- Budou, Kiwi, Rose Attacker
- Donguri, Rose Attacker
- Matsubokkuri, Sakura Hurricane
- Durian, Sakura Hurricane
- Arms Change:
- Lock Vehicle:
- As part of Super Hero Time, this episode aired alongside Zyuden Sentai Kyoryuger episode 41 Brave 41: Yanasanta! Deboss' World War.
- Viewership: 6.1%
- Closing Screen Lockseed Collection:
- This is the first time that all seven original Armored Riders are seen transforming in one episode.
- The Sakura Hurricane Lockseed held by Oren is much smaller than the prop size (This always happen on all Kamen Rider shows as the actors holds the device are smaller, but as Riders, the device becomes larger). This is because what Oren is holding is the toy version, the DX Sakura Hurricane Lockseed itself.
Kamen Rider Gaim Volume 3 features episodes 9-12: The Monster Inves Capture Battle!, Rider Great Assembly! Revealing the Mystery of the Forest!, The Truth Behind the Christmas Game and New Generation of Riders Appear! 
- TV Asahi's official summary for 「ライダー大集結！森の謎を暴け！」
- Toei TV's official episode guide for 「ライダー大集結！森の謎を暴け！」