All the Worlds Are a Stage

This is when levels come Back for the Finale. The final level is made of parts from and/or in the theme of most to all past levels, or at least it has a section like that. It's a good way to extend the final level and make it feel more epic, as the player is required to revisit their past challenges. There are a few guidelines for this trope:

The level parts may or may not be lifted directly from the levels they are from, but they do have to include enough distinct design elements and/or distinct gameplay (such as types of platforms or vehicles); including the unique enemies encountered there can help support the argument. (If there's something that directly tells you it's a part based off a level, like a sign or symbol, then it's indisputable; however, if the content doesn't match the label, the developers had better have some good reasons when accused of false advertising.)
The level parts can be encountered linearly, at the player's choice, or a mixture of both (with a forced starting or finish level part, for instance). If linearly, they may or may not be played through in the same order as played through in the game.
The level parts can be jammed together or separated with novel content connecting them together. The new content, basically the actual final level itself, has a theme different from the others—for instance, that Very Definitely Final Dungeon theme you were all but promised in the above situation. As such, it doesn't matter whether or not you enter the final level itself in an original part or a level part.
This trope does not need to apply to the entire final level; in this case, it's usually just a major area where the level parts are all together.
If the level parts don't have visual elements from the past level they're from, they at least have geography/layout from the level. Think of it as reskinning a level.
Just because you're revisiting past stages you got the items and abilities from already doesn't mean you're going to find nothing new to grab. Don't get your hopes up, though.

Next, this trope comes in a few different flavors.

Memory Lane: Within the final level, there's an area comprised of linear, jammed-together or in-rooms/warped-to level sections. Bonus points if the level sections are direct extractions (with possible changes). Often has players using the item/ability they got in a level a lot during that level section.
Ganon's Tower: Nonlinear Memory Lane. Named for the final dungeon in The Legend of Zelda Ocarina of Time, the first half of which consists of an in-rooms version of this. Sometimes leads to boss re-fights.
World Terminus: Memory Lane with direct extractions, but they're actually just arenas for gauntlets where you have to fight a horde of enemies to clear each level section. Named for the area in the first Kingdom Hearts.
Final Exam Stage: A natural method of doing a final level, the Final Exam Stage places the player at the start of a linear Death Course comprised of level parts, often in game order, often challenging them to apply everything they have learned and gained as they go along. This makes up the entire final level. The level equivalent of the Final Exam Boss.
Multiple-Choice Final Exam Stage: Nonlinear Final Exam Stage.
Muscle Memory Lane: Unique (usually platforming) sections from previous levels appear, but you won't notice at first, because the aesthetics pretty much otherwise fit with the main final stage. Then you play it and it feels familiar. A cool bit of subtlety that has to be fairly obvious to qualify. Guideline #5 in action.
Zant Stage Rush: You're fighting the final boss when, suddenly, you're warped to a location in a past stage for some reason or another. You go back to the main ring before going to the next level section, or you progress to them one after another. Often an illusion. Named for the fight against Zant in The Legend of Zelda Twilight Princess.
Viewtiful Joe Boss Rush: Kind of reaching, but...A Boss Rush where you start out in the beginning of the room they're in (or a facsimile) before fighting each one. Named for the style of Boss Rush in the main Viewtiful Joe series.
Remember Me Level: When a level so old, it's from a previous game, is used. Only applies when said previous game is from earlier in the same storyline/character's history.

Related tropes include The Very Definitely Final Dungeon, which this trope often still has elements of, and Hailfire Peaks, going along the theme of different terrains in one level. When it's made, the trope for any level with more than two types of terrain (Hailfire Peaks but more) will be a supertrope.

The trope name is a play on "All the world's a stage", the famous Shakespeare quote from As You Like It.

Examples of All the Worlds Are a Stage include:

Castlevania Aria of Sorrow has the Chaotic Realm, made up of various parts of all the previous areas.
Sonic the Hedgehog 2006 has the infamous End of the World stage, set in seven of the nine previously played levels as the world gets more screwed up. Final Exam Stage type.
- Scrap Brain Zone from the original Sonic the Hedgehog has enemies from the game's previous stages. In addition, Act 3 is a re-colored, more difficult version of Labyrinth Zone.
- Eggmanland in Sonic Unleashed is a giant gauntlet of some of the most difficult platforming challenges from both the Sonic and Werehog sections, including most of the game's enemies, a bobsled-esque portion like one from earlier in the game, a skydiving section, and generally recalls all your abilities that you've needed to use.
Most Dragon Quest Bonus Dungeons are made up of repeated parts of other dungeons.
Chocobo's Dungeon for Wii also had this in the Bonus Dungeon. Justified as the theme was memories and the Bonus Dungeon was about Chocobo's memories—which of course would include the dungeons he explored during the game.
In Legend of Dragoon, the final level consists of elements of previous areas put together.
The Great Maze from Super Smash Bros Brawl is a mashup of previous levels, all interconnected. Integrated with the story, as these levels were captured by Subspace bombs throughout the game (before this point, the assumption was that the areas were just blown-up, but it turns out Subspace bombs are different). Multiple-Choice Final Exam Stage type.
Halfway through Magicka you fight the Big Bad in a "mental battle" which consists of teleporting through several islands and defeating groups of mooks. Zant Stage Rush type.
A Super Mario World Central Production has this in Bowser's Castle—specifically, the part where you first enter the Void. You can go through any room of your choice. Each is thematically based on the eight main worlds of the game, but there are new gimmicks present (for example, spin jumps in the Mountain room switches on/off the red and blue blocks). Ganon's Tower type.
Kingdom Hearts is the source of the World Terminus type.
A variation: the lower-left corner of the World Map in Zelda II the Adventure of Link is based loosely off of the first game's Hyrule.
The Legend of Zelda Ocarina of Time is the source of the Ganon's Tower type. Has six sections on the bottom floor corresponding to each medallion. (Interestingly enough, this means the only one that actually isn't a past dungeon is the Light Medallion section, as there is no dungeon to get that medallion.)
The Legend of Zelda Twilight Princess is the source of the Zant Stage Rush type. Zant teleports you to arenas from a number of past dungeons and imitates the boss or miniboss in some way.
The Legend of Zelda Majoras Mask has the moon as an example of the Ganon's Tower type. You go through mini-dungeons themed after the main four dungeons of the game.
- Noteably, all 4 of these are optional. That said doing them all and handing over every mask awards the infinity+1 mask
The Legend of Zelda the Wind Waker has Ganon's Tower. Guess which type it is. (Zelda likes this type, apparently.) Has Dragon Roost Cavern, Forbidden Forest, Earth Temple, and Wind Temple sections before you must fight the boss. You are also reduced to whatever items were available to you when you originally went through the dungeon. Also crosses over with the Viewtiful Joe type as at the end of the segments you fight a black-and-white version of the respective boss for the original dungeon, complete with reconstructed boss rooms.
The Legend of Zelda Skyward Sword has Sky Keep, which is yet another Ganon's Tower type. Except for the entrance lobby and the Silent Realm rooms where you collect each piece of the Triforce, every room has the aesthetics and music of all the previous dungeons.
Viewtiful Joe is the source of the Viewtiful Joe Boss Rush type.
Rocket Robot On Wheels contains Jojo's World, a gauntlet of the Final Exam Stage type.
Prince of Persia: The Two Thrones has this at the end during the final battle, having the Prince revisit places in his past. Zant Stage Rush and Remember Me Level types.
Goemon's Great Adventure has Dream Castle, which is a merciless mashup of segments based on the previous four castles. The really hard parts. Final Exam Stage type.
Kirby's Dream Land uses the Ganon's Tower type in Mt. DeDeDe, with doors leading to areas based on the previous stages, as well as rematches against the bosses, that you have to go through to reach the last boss.
Kirby's Adventure features a variant of the "Remember Me Level" in Stage 7-6. The backgrounds and music are borrowed from Kirby's Dream Land, but the stage segments are not copied from areas in the original game. And Kirby himself remains pink, although almost everything else is Deliberately Monochrome.
Super Paper Mario has such a sequence near the end where the protagonists pursue Dimentio through sections of previous levels. The pause menu even says which level you're in.
Tiny Toon Adventures: Montana's Movie Madness has a Final Exam Stage type, putting you through four mini-stages (literally and figuratively: there are spotlights and movie cameras scattered around them) themed off of the previous levels before going up against the final boss.
Sanitarium has a penultimate Memory Lane subchapter called "The Gauntlet" right before the final Puzzle Boss subchapter with Dr. Morgan. In it, you find yourself in a mishmash of elements of all of the earlier non-"real world" chapters. Not only that, but to solve various puzzles you have to switch between Max and all of his alter-egos as well.
The first game of Death Jr. has its final level as the Memory Lane typege
The sequel to the NES game StarTropics is one of the rare "Remember me levels" in that the last stage of the game has you return to the first stage of the first game. There's even an undead version of the first boss of the first game.
Final Fantasy V has the path to the depth of the Void, which is said to consume the world and so contains many locations that, if they aren't the actual previous locations that have been absorbed, are similar to previous locations.
Final Fantasy VI features this in Kefka's Tower. The tower itself is mostly a collection of ruins, but there are elements of the destroyed Imperial capital of Vector and the Magitek Factory, and some rooms are exactly like they were when the player first visited them.
Final Fantasy Mystic Quest has Doom Castle, where each of the four floors the player visits are thematic recreations of the final dungeons of the four regions, complete with powered-up versions of their bosses.
A lot of Mega Man games have the Viewtiful Joe-style Boss Rush.
- Interestingly, Mega Man 5 is the only game that had the sense to actually reuse the original rooms you fought the bosses in, complete with the Boss Corridor door behind Mega Man.
- Mega Man 10's Wily stages consist mostly of elements and enemies from the Robot Master stages, all mashed together. These stages frequently combine something from one stage with something from another to make a more difficult combination.
The fight against Xion in Kingdom Hearts 358 Days Over 2 is one of the Zant Stage Rush variety.
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Silent Hill 1 has Nowhere, which is mostly comprised of corridors reminiscent of the Alchemilla Hospital connecting rooms from other parts of the game, such as Midwich Elementary School's classrooms and the Green Lion Antique Store.
The final form of Lavos in Chrono Trigger randomly switches between time periods, the psychedelic background taking on the image of an area in that time period while Lavos uses attacks particular to enemies found in that era.
In the later stages of Freedom Force, Time Master produces opponents and backdrops from earlier in the game to harass our heroes.
The final platforming level of Stinkoman 20 X 6 takes everything from the rest of the game and throws it in a blender. Everything is a mishmash of stuff that has been seen before, such as the ground being made of the ground sprites from all the previous levels all next to each other, both kinds of ladders, and music which mashes it all together. Add in some wonky behavior (it is supposed to be a glitch level) and a boss made of platforms, spikes, and monsters, and you have the recipe for an epic finale.
In Shin Megami Tensei: Strange Journey, the penultimate sector, Grus, is made up of sections patterned after all of the previous sectors, changing from area to area with no apparent pattern to it.
In Athena, the final world is made up mostly of bits and pieces of the previous levels strung together, including the bosses.
Tasty Planet Back for Seconds has multiple Final Exam Stages with an added twist ending in each.
The final boss fight in Battle Golfer Yui takes place on various golf courses from the previous matches mixed in new courses.

Ah, but the memories.