Scenery as You Go

The main character is walking through The Very Definitely Final Dungeon, and approaches what appears to be (let's say) a broken bridge! Is this a Broken Bridge, or is it the variety of Locked Door where you need to find a completely alternate route? It's neither—as you approach it, rocks and bits of masonry magically float up from the chasm below, constructing the bridge before you—sometimes only creating part of it, and adding more as you keep going!

It doesn't have to be a bridge, per se, but it must (a) allow the main character to progress to the next area with no other means of getting there, and (b) occur independently of the character's own actions, except that he's simply approaching it. So the scene from the X-Men movie where Magneto creates his own platforms doesn't count.

Examples of Scenery as You Go include:

Makes an appearance several times, mostly in the Black Throne, in Darksiders.
In Devil May Cry 3, just as you enter the Demon Realm, you might expect a jumping puzzle... and then the oblong Floating Platforms slam together to form a path as you approach.
In Prey, this happens with entire rooms near the end.
In Doom 3, in Hell, at one point you're stuck on a floating platform the size of a city block until you kill a bunch of Imps, at which point a bridge creates itself leading to a nearby structure, though that's more an example of "kill all monsters to open the Locked Door".
In Super Mario Galaxy, a jumping puzzle involves this in the Space Junk Galaxy, as Mario moves around an invisible maze that appears as he goes while collecting star fragments on a timer.
- There's a much bigger puzzle of this variety for Space Junk Galaxy's Purple Comet. Ten groups of Purple Coins scattered across a huge field with more complex paths. And the black hole below it appears to be bigger, but like the first puzzle, as long as you don't fall off, you're fine.
- And in the final level, during one of the 2D gameplay segments, there will also be blocks being summoned up that you'll have to make use of. Mind you, they also disappear again if you're not moving fast enough.
- Super Mario Galaxy 2 also has the Space Junk example on one of the rolling balls, which are very difficult to stop when the materializing path takes an unexpected corner.
In the first Prince of Persia game, after merging with the Shadow, you are faced with a gap that would appear to be insurmountable even with a running jump. Run across it, and floor tiles will instantly appear.
This also happens in Clive Barker's Undying, in the floating city of Oneiros. At several points you will see a floating platform of some sort, far out of reach of any jump, and a path on your current platform seemingly leading off into oblivion. Walk towards the end of it and, just as you reach the edge, floating tiles will appear.
In Final Fantasy XII, Giruvegan and the Great Crystal are full of walkways that materialize just as you step on them.
American McGee's Alice does a variant on this in a couple of rooms. A path over infinity leapfrogs over to you, making a path as you go. And behind you, the path is disintegrating at a somewhat alarming pace!
The rainbow bridge to Asgard in Valkyrie Profile 2 seems to only actually materialize where you're actually standing. As you run, it materializes under your feet, and disintegrates behind you.
The gimmick of the custom Unreal Tournament 2004 map "DM-Reconstruct" is this very trope.
In Kingdom Hearts 2, Sora & Co. run into a great chasm within The Very Definitely Final Dungeon. A shimmering staircase materializes beneath their feet as they cross it, stopping only to do battle at every landing.
Ico has two of these in the reflector buildings.
The Last Remnant has architecture that shifts around allowing you to advance in The Sacred Lands and beneath Undelwalt.
Halo's Light Bridges. Pointless, solid, bright, and always off, they are turned on by you.
Starlight Carnival Zone from Sonic Colors, in certain areas.
The Highways of Iacon City in the Autobot campaign of Transformers: War for Cybertron. Story-wise, they were reactivated offscreen by your allies, but once you're cruising down them, they automatically construct themselves in front of you as you drive.
One sub-mission in Mondo Agency has a maze of floating tiles that appear when approached by the player or laser indians.
In Will Rock, during the last level, Zeus is nice enough to provide you a stair of floating platforms leading across a HUGE lava-filled chasm and to his lair. However if you're not fast enough the platforms will crumble.
Occurs at one point in The Elephants Dream, with small metal platforms on robotic arms rising from the darkness below the characters.
Bastion does this from the very beginning. The narrator even mentions it.
In the Metro 2033 game, Artyom is trapped in a psychic maze by the Dark Ones and this is how the last area manifests. Notably, running too fast, before allowing the path to fully form can actually kill you as you fall into the abyss.
In The Legend of Zelda Skyward Sword, the Timeshift Stones can turn quicksand into traversable ground and make rocky outcrops spring from the ground.
The last room in Windosill is in what appears to be an unfinished colosseum, or a construction of one. When you drag the toy train up the outside spiral of the colosseum, the unfinished sections suddenly float up and become a rigid road.