Thwomp

Thwomps are large stone creatures that hide on ceilings until Mario passes under them, and they will fall down in an attempt to crush him. They are usually either blue or gray in color, and may be covered in spikes.

Appearances
Thwomps first appeared in castle levels in Super Mario Bros. 3, where they were covered in spikes, and Mario would die after simply touching them. They appeared again in Super Mario World and were exactly the same, but there was also a new variety of Thwomp called a Thwimp that could move freely while going up and down, and was much smaller then a normal Thwomp. Thwomps appeared again in Super Mario 64, where they had no spikes, and would keep going up and down instead of only crashing down when Mario went under them. They were used mainly to get to higher places. Another related creature called a Whomp also appeared in Super Mario 64. Whomps can walk, and they try to fall face first on Mario.

Thwomps also appear in Super Mario Galaxy, where they appear to be more than double the size they were in other games.

Mario Kart
Thwomps appeared in Super Mario Kart's Rainbow Road, and would crush racers if they got too close to them. In most Mario Kart games, they have appeared in Bowser's Castle courses. The most notable one was in Mario Kart 64, where they filled almost the whole castle and were tricky to get past. Including a greenish hyper one locked in a cage. There are also thwomps that laugh evilly.

Mario Party
In Mario Party games, Thwomps appear as both a trap and an item. The item will make it so that, if an opponent passes the space that the item was used on, they will stop moving. If someone lands on the turn with the trap, they will be stuck on that space for a turn.

Mario Strikers Charged
Thwomps appear as obstacles in The Sand Tomb, a field in Mario Strikers Charged.

Super Smash Bros.
Thwomps appear as a trophy in Super Smash Bros. Melee. Kirby also turns into one sometimes when using "Stone".

Trophy Description
Thwomps spend most of their time suspended in midair, waiting. When Mario passes below, they crash down with amazing speed. As you may guess from their appearance, they're heavy and solid enough to make any attack on them futile. Small ones are called Thwimps: despite their weight, they often form groups and bounce around.

New Super Mario Bros.
Thwomps are found only in certain castles such as world 4 or the final castle.under them are usually x blocks warning you where they will crash.

Mario and Luigi: Partners in Time
There is a time hole on the third floor which leads to Thwomp Volcano, where evil thwomp-like blocks appear as common enemies (as well as other places). Also Mrs. Thwomp, a roundish, rockish thwomp appears as a boss, her husband as a transport to inside and outside of the volcano, thwomps appear as hosts for minigames inside the volcano, and a thwomp is an elevator to get down the floors. If you return later, you can't use this elevator as it crashed on the floor you fought Bowser and Baby Bowser.