Impossible coins
Impossible Coins are coins that are impossible to collect. These are usually created through programmer oversights.
Current Impossible Coins
Second THI Impossible Coin
In Tiny Huge Island there is a row of coins, one of which spawns too low below the ground and the game immediately unloads it 1 frame after it loads since there is a failsafe stopping it from loading for more than 1 frame. This makes it so that instead of 5 coins, 4 coins load. Though it is loaded for one frame, it may not be cloned because cloning and then collecting requires at least 2 frames.
Mystery Goomba
The Mystery Goomba is a member of a goomba triangle in Bowser in the Sky that is placed over a pit, causing it to instantly descend to the death barrier upon being loaded. Thus, it exists in a location that cannot be reached. In addition, the radius of the Goomba triangle and the Mystery Goomba do not overlap, so it turns invisible and intangible after one frame and doesn't move. While it is possible to clone the Mystery Goomba, for all intents and purposes the coin inside the real thing has been deemed an impossible coin.
Former Impossible Coins
The Impossible Coin
This coin is a coin in THI that was thought for a long time to be impossible to collect. It is part of a row of coins, but the row is placed too low and the coin appears under the ground.
The coin was initially discovered in January 2002 by GameFAQs user Josiah. Many attempted to collect the coin, and no one was able to. For this reason, it was dubbed "The Impossible Coin."
In 2014, Twitch streamer MisterMonopoli recognized Pannenkoek2012 in his stream's chat, and asked him to try to collect the coin. Pannenkoek2012 successfully collected the coin by clipping inside of the island, swimming, jumping, and kicking to the coin. He did this and uploaded a video of it on June 12th, 2014, calling it, "SM64 - Collecting the Impossible Coin".