''Franchise/KamenRider Series/KamenRiderFourze & [[Series/KamenRiderOOO OOO]]: Movie War Mega Max'' is the third Movie War movie. Premiered in Japanese theatres on December 10, 2011.

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!! This movie contains examples of the following tropes:
* AllThereInTheManual: The names of Michal's Kamen Rider forms. The evil form that uses core medals is called Kamen Rider Poseidon, and the good form created from the water-powered belt is called Kamen Rider Aqua.
* BigBad: Lem Kannagi of [[Series/KamenRiderDouble Foundation X]].
* {{Crossover}}: As the name of the movie suggests, it's a crossover between ''Series/KamenRiderFourze'' and ''Series/KamenRiderOOO''. However, [[Series/KamenRiderDouble Kamen Rider Double and Foundation X]] are featured as well, uniting the first three leading riders of the Neo-Heisei era. In the wake of ''[[Film/OOODenOAllRidersLetsGoKamenRiders OOO, Den-O, All Riders: Let's Go Kamen Riders]]'', 2011 being the fortieth anniversary year of the series, the original seven Kamen Riders ([[Series/KamenRider Ichigo, Nigo]], [[Series/KamenRiderV3 V3, Riderman]], [[Series/KamenRiderX X]], [[Series/KamenRiderAmazon Amazon]], and [[Series/KamenRiderStronger Stronger]]) play a major role as well, where they are now known as the Seven Legendary Riders.
* EarlyBirdCameo: As each Movie War movie has featured the introduction of the upcoming [[SixthRanger Secondary Rider]] of the current show, Kamen Rider Meteor makes his first appearance at the end of the movie.
* [[spoiler:EleventhHourRanger: Kamen Rider Aqua returns in the final act of ''Movie Wars'', coming back to present time to help the Riders against Foundation X's forces, and giving Eiji the Super [=TaToBa=] medals.]]
* LegionOfDoom: Foundation X uses the research its agents gathered to build an army consisting of various MonstersOfTheWeek as well as mooks from the three series ''Fourze'', ''OOO'' and ''W'', alongside monsters of the BigBad's own design, called "Mutamids". They're not actually the same monsters from their original series, but it's [[PropRecycling an excuse to reuse monster suits]].
* SealedGoodInACan: The Seven Legendary Riders are sealed inside Fourze and OOO's [[TransformationTrinket transformation trinkets]] by Kannagi. Ichigo, Nigo, V3 and Riderman are trapped within Astro Switches while X, Amazon and Stronger trapped inside Core Medals. They are freed when Fourze and OOO perform a Limit Break and a Scanning Charge respectively.
* SuperMode: OOO's Super [=TaToBa=] Combo and Fourze's Rocket States.
* WhyDidItHaveToBeSnakes: Ironically, despite being a water-themed Rider, Michal is afraid of water. [[spoiler:He manages to overcome it in the end.]]
* TheWorfEffect: The Seven Legendary Riders are hit with this to show how dangerous Foundation X's threat is here in the movie.