No, Mareep cannot evolve with the use of a Thunder Stone.
Mareep will evolve at Level 15 in Pokémon Crystal.
Mareep evolves into a flaafy,then Flaffy evolves into Amporas
Evolve from Mareep. You get Mareep on Route 32
lvl. 15.
it evolves into ampheros
Mareep evolves into Flaffy a Lv 15 then into Ampharos at Lv 30.
The same thing that its supposed to evolve into.There is no evolution cheat in existance
Into Flaaffy at Level 15 and into Ampharos at Level 30.
catch mareep, then evolve it into flaaffy, then evolve it into ampharos. amphy is ampharos.
Just evolve a mareep
mareep evolves at level 15 then at level 30 in Pokemon crater