"Encounter! Wild Pokémon (Legacy Mix) - Pokémon GO" is a high quality rip of "Encounter! Wild Pokémon" from the game Pokémon Go.
This rip is a chiptune remix of the original "Encounter! Wild Pokémon" theme, but then at 0:37 it switches its melody to one part of the Johto Trainer Battle from Pokémon Gold & Silver, and also "POKEMON GO SONG!!!" cuts in at 0:59 and 2:13.