Bottomless pit

Pits (or Bottomless Pits) are hazards that appear in nearly every Mario game. They are very common and found in mostly every level in a certain Mario game. Pits are mainly the cause for Mario's defeats in most of his games leading to Game Overs.

Super Mario Bros. series
Pits are first seen in Super Mario Bros. on the very first level and they appear in the rest of the Super Mario Bros. games. Mario can simply jump over the pits in order to avoid them. However, some pits require Mario to build speed in order to jump over them. In rarer cases, Mario must jump over a bunch of enemies in order to cross a very wide pit.

Super Mario World
Pits appear in levels in this game. Bottomless pits are very common in the Special World levels where some are spaced together attempint to get Mario or Luigi to fall through. Mario or Luigi can easily use a Cape or Flying Yoshi to safetly cross pits but must avoid enemies to keep their flight.

Super Mario 64
Pits are actually found on a few levels in this game mainly Tall Tall Mountain and Rainbow Ride. Mario must jump platform to platform in order to avoid deep plumments.

Super Smash Bros. series
Bottomless Pits play a semi-big role in this game series. Players who can utilize the Meteor Smash techinque have a great chance of smashing an opponent down into a pit. In Super Smash Bros. Brawl, pits are very common during Adventure Mode.

Paper Mario series
Bottomless Pits are actually rare in the Paper Mario games. None really appear in Paper Mario but they do become somewhat common in Paper Mario: The Thousand Year Door, Super Paper Mario, and Paper Mario: Sticker Star. If Mario falls down a pit, he then loses 1 HP and is put back in front of the pit he fell in.

Trivia

 * One of the residents of The Underwhere from Super Paper Mario said his game ended after falling into a pit.