Falling spike

Falling Spikes are spiked obstacles that fall from ceilings, and were introduced in Super Mario Land (although the Icicle from Mario Bros. can be considered a precursor). During this game, a lone Falling Spike appears in the Easton Kingdom, specifically 3-2. In comparison to later examples, this one moves rather slowly, and resembles a conjoined pair of stalactites. Many such stalactites appear on the ceiling of this stage, without falling. Even after this one falls, the stalactites appear to remain on the ceiling.

Super Mario World
In Super Mario World, Falling Spikes are found only in Castles and Fortresses, and are typically grouped together with standard Spikes. They are slightly off-color compared to normal Spikes. Unlike Icicles, Falling Spikes will remain on the ceiling until Mario or Luigi approach one, which will trigger it into falling, similar to a Thwomp. Once it falls, a Falling Spike will continue to fall through the floor until it disappears. If the player goes out of range and back again, the Falling Spike will return.

Super Mario Land 2: 6 Golden Coins
Falling Spikes also appear in Super Mario Land 2: 6 Golden Coins in the Pumpkin Zone.

Donkey Kong (Game Boy)
Falling Spikes reappear in the Game Boy Donkey Kong and Game Boy Advance Mario vs. Donkey Kong. This time they get stuck on the floor after they fall. Mario or a Mini-Mario can use its flat end as a platform. After a few seconds it will disappear and regenerate in its original location.

Super Mario Advance 4: Super Mario Bros. 3
Falling Spikes also appear in Super Mario Advance 4: Super Mario Bros. 3, in the level Bowser's Last Stand. While they act as they did in Super Mario World, they look the same as normal Spikes.