beach: pidgey, doduo, surfing pikachu/pikachu on a stump, butterfree, lapras, snorlax, meowth, scyther, magikarp, eevee, chansey, kangaskhan.
tunnel: pikachu on a ball, electrode, electabuzz, kakuna, zubat, zapdos, magikarp, haunter, diglett, dugtrio, magnemite, magneton.
volcano: rapidash, vulpix, charmander, magmar, moltres, growlithe, arcanine, charmeleon, charizard. (you may find a magikarp in the water near the growlithe/arcanine craters)
river: poliwag, bulbasaur, shellder, slowpoke, slobro, vileplume, magikarp, metapod, psyduck, porygon, cloyster, speed pikachu.
cave: zubat, grimer, bulbasaur/ditto, muk, koffing, weepinbell, victreebell, pikachu on balloons, jynx, articuno, pikachu on articuno, jigglypuff trio on stage.
valley: squirtle, geodude, sandshrew, magikarp, graveler, sandslash, staryu, gyarados, starmie, dratini, dragonite, goldeen.
Rainbow Cloud: Mew.