You can evolve Pokémon by buying a specific item. When they evolve, they only gain 1 AP, so don’t expect a big improvement, it’s just a small easter egg. The items are as follows:
Pikachu - Thunder Stone
Cubone - Thick Club
Scyther - MetalCoat
Marill - Fresh Water
Sneasel - Razor Claw
Croagunk - Black Sludge
Riolu - Soothe Bell
Cacnea - Soft Sand
Taillow - Silver Wing
Shinies appear randomly with a 1/100 chance. They’re Pokémon with alternate colors and give extra money and points when defeated.