SingleOrDefault will return a single Tamagutchi, so the result is not an IEnumerable at all. Perhaps you mean
public Tamagotchi Get2()
{
var _result = Gotchis.SingleOrDefault(tama => tama.Name == "VLW");
return _result;
}
or
public IEnumerable<Tamagotchi> Get2()
{
var _result = Gotchis.Where(tama => tama.Name == "VLW");
return _result;
}