From Glitch City Laboratories
The Horn Drill Glitch is a glitch in the Generation II Pokémon games, which causes the move Counter to deal infinite damage when Horn Drill is used by the other Pokémon and misses.
This is considered a glitch for two main reasons: one is that in Generation II, Horn Drill is the only one-hit knockout move compatible with this glitch. The second is that in Pokémon Stadium 2, the glitch no longer occurs, both reasons suggesting that this was unintended.
- A Pokémon that knows either Horn Drill or Counter.
- Another Pokémon that the above will fight, which knows either Horn Drill or Counter (whichever the other one doesn't know.)
- Have Horn Drill and Counter be used by the Pokémon in the same turn, and have Horn Drill miss.
- The Counter-using Pokémon will deal infinite damage to its opponent.