Fake Platform

The Fake Platform appears to be solid, but doesn't support your weight for even a moment if you land on it. Unlike the Temporary Platform, which you can run across or jump off of, the Fake Platform drops you instantly if you set foot on it. Usually, this is over a Bottomless Pit or Spikes of Doom.

Annoying even if you know it's a trap, because it tends to restrict movement in ways that empty air in the same spot wouldn't.

Yet another type of Malevolent Architecture. May result from Depth Perplexion.

The typical Platform Hell game is loaded with these, but will only ever spring them on you when you least expect it.

Film

 * Appears in Indiana Jones and The Last Crusade. Tiles that don't spell out Jehovah (with an I) are fake and will drop you into a deep pit.

Video Games

 * The trapdoor blocks in Lode Runner, which you couldn't run into from the side. The one way to test for them was to stand next to an apparently diggable block and try to dig through it.
 * The rotating tiles in the Temple of Doom portion of Prince of Persia 2: The Shadow and the Flame, which usually led to a fatal fall or a Death Trap. Like the loose tiles, jumping up and down would reveal their locations. Unlike the loose tiles, you couldn't drop them and then mantle off.
 * The Unfair Platformer has too many of these.
 * Platforms that open from under you occur throughout La-Mulana, but not often enough to contribute significantly to the game's difficulty (though one in the Chamber of Birth can set you back to the beginning of an annoying maze). That is, until you get into the Hell Temple and find yourself falling into the Land of Hell again by stepping on what looked like a perfectly solid platform. Throwing bombs and the throwing knives as well as watching enemy movement patterns help sort out the fake platforms from the real ones here.
 * In Twilight Princess, in order to get to the Big Bad, you had to go through a room full of these. Changing into your wolf form lets you see ghosts that point the way; aside from that, all you can do is avoid the ones that killed you last time.
 * Appear in several occasions in Super Metroid, usually immediately before an upgrade.
 * Or a boss fight. Or both, as the bosses/minibosses tend to guard said upgrades.
 * Actually, most, if not all, are Temporary Platform. They disappear so quickly, however, that is essencially this trope, anyway.
 * And they come back to block you which makes it annoying if you're trying to jump back up, like with the Space Jump.
 * Using illusions to do this is a favorite of evil DMs in Dungeons and Dragons
 * I Wanna Be the Guy has at least one of these in the area after the Koopa Klown Kar fight. You have to jump to the one square on the left side of the platform that won't collapse. Land anywhere else on it and you'll immediately fall to your death. Also, there are sections of ground after the Mecha Birdo fight and above the "Incinerator of The Guy" that aren't necessarily platforms, but will spin around and immediately let you drop down (leading to your assured death in the former case) if you don't jump over them.
 * Appears in several Mega Man games. When they do appear, they can usually be detected by using a weapon that travels along the ground, which will fall through the ground when it reaches the false part of the floor. Mega Man 9 has enemies that create fake platforms in a few stages.
 * Some of the stages have trapdoor platforms.
 * Several places in the Ty the Tasmanian Tiger series have such lovely elements of game design. In the third one, there's an optional maze of the blasted things. The object you acquire is considerably less than worth it, if not quite on the level of And Your Reward Is Clothes.
 * In Within a Deep Forest, in the sub-level Shadowlands, one particular area has floating platforms that disappear right before you can touch them, indicating their false nature. Conversely, the solid platforms that you actually climb on are invisible until you're right on top of them (or more likely, underneath them, causing you to rebound back down to the ground).
 * The classic Crash Bandicoot did this with the level's "High Road" and "Bridge to Nowhere" in which there were 4 types of planks to jump on, Solid ones, planks that break after a couple seconds, planks that cause you to slide and make climbing up more difficult and finally the instant break plank or the fake platform.
 * Cleverly implemented in Sonic Adventure 2: In Eggman's section of the final stage, there is a floating platform in the middle over a gap, followed by an alcove on the other side. When you land on the platform to try to go to the other side, it immediately drops; the area it drops to is the area you're supposed to go down. The clever part is getting across; the entire level deals with switches that stop time, so if you backtrack a little to a completed puzzle, activate the time switch, and go back, the platform won't fall (because time is frozen), allowing you to get to the other side.
 * One of the trap types in Evil Genius.
 * Standard fare in Castlevania II, as discussed/raged on at length by the AVGN.
 * The first Commander Keen game had blocks, often just before a key card, that Keen could fall through but not jump back up through.
 * In the Jumper series, there are blue blocks. These blocks fall less then a second after you land. The time you have to move off is so close to instantaneous that to call them Temporary Platforms would be being generous.
 * You can't jump on broken platforms in Doodle Jump; you simply fall through them.

Web Comics

 * Although usually a video game trope the main character of Cwens Quest runs into one of these when she steps onto the edge floating island.
 * And now a more direct example.