From Glitch City Laboratories
Within the Generation I Pokémon games, it is possible for the player to essentially walk around with a party of no active Pokémon if he or she deposits all Pokémon into the PC except those which are fainted.
If the player then walks three extra steps he or she will recieve a black out, however the amount of steps required for this to happen can be reset if the player then saves the game and performs a soft/hard reset. In this way, by saving the game oftenly the player will eventually be able to enter a trainer battle. This is currently the only known method of activating the phenomenum Wild appeared! for when the player enters a battle with no Pokémon in Generation I without the use of a game-altering device.