Clefa and those baby Pokemon from generation 2 like:
Magby
Pichu
Smoochum
Igglybuff
Togepi
etc. need to be pampered to be able to evolve. To make them happy you should have them in your first slot in your party, do not let them faint, feed them berries and poke blocks, groom them, level them up
All these activities are disliked by Pokemon and should be avoided when aiming for happiness:
Putting them in the PC Box
Giving them potions (they are bitter, berries taste much better)
Letting them faint in battle
Keeping them fainted for a long time
Leaving them in daycare
Chat with our AI personalities
Wild Clefa, Clefairy and Lunatone have 5% chance to hold it, you can dig in Sinnoh Underground or trade with someone.
Sun Stone -use on Sunkern to evolve into Sunflora and on Gloom to evolve into BellossomMoon Stone-use on Nidorina to evolve into Nidoqueen, Nidorino to evolve into Nidoking, Jigglypuff to evolve into Wigglytuff, Clefairy to evolve into Clefable or Skitty to evolve into DelcattyFire Stone-use on Eevee to evolve into Flareon, Growlithe to evolve into Arcanine or Vulpix to evolve into NinetalesThunderstone-use on Pikachu to evolve into Raichu or Eevee to evolve into JolteonWater Stone-use on Eevee to evolve into Vaporeon, Staryu to evolve into Starmie, Shellder to evolve into Cloyster or Lombre to evolve into LudicoloLeaf Stone-use on Gloom to evolve into Vileplume, Exeggcute to evolve into Exeggcutor or Nuzleaf to evolve into ShiftryShiny Stone-use on Togetic to evolve into Togekiss or Roselia to evolve into RoseradeDusk Stone-use on Misdreavus to evolve into Mismagius or Murkrow to evolve into HonchkrowDawn Stone-use on a Female Snorunt to evolve into Froslass or a male Kirlia to evolve into a GalladeOval Stone-Happiny has to hold during the day to evolve into Chansey
Gastrodon doesn't evolve.
Five different Pokemon evolve using a Sun Stone. Gloom will evolve into Bellossom. Sunkern will evolve into Sunflora. Cottonee will evolve into Whimsicott. Petilil will evolve into Lilligant. Helioptile will evolve into Heliolisk.
it does not evolve