The invisible tree glitch is a glitch in Pokémon Red, Blue and Pokémon Yellow where a tree that the player has just cut down comes back, invisible, and blocks the player like a visible tree.
1. Go to Route 14, east of Fuchsia City.
2. Walk past a group of trainers, and the player should come upon a cuttable tree.
3. Cut down the tree and take four to five steps to the left from where the tree was.
4. Walk back to the tree. The tree will look as if it has been cut down but the player will not be able to walk through it. It is possible to remove the tree by using Cut, making the tree reappear when the "(POKéMON) hacked away with CUT!" message appears.
After the player takes four steps left from the tree, the map changes from Route 14 to Route 15. If the tree goes off the screen (this happens when the player walks more than five steps to the left) its graphics will be reloaded when the player returns and the glitch will not occur.
YouTube video by Zachtheglitchbuster.