In pokemon crystal, when you click the pokegear, the buttons at the top are slightly streched. The pokedex is a mess, the list of pokemon is pretty blurred.
When the battle animation screen appears,
1) there are artifacts present in the enemy pokemon's animation (rarely).
2) when the player and enemy are crossing the screen (right at the beginning of a battle) there are sometimes black boxes around the enemy. some examples are rattata and pokemaniac.