Do you need to trade Boldore to reduce the candy requirement for evolution to zero?
Solution 1:
In Pokemon Go, it is a bit different implemented than the original series. I traded a Roggenrola with a friend (so not a Boldore), evolved the Roggenrola myself, and then evolved it freely to Gigalith. So you do not have to trade the form that gets the free evolution. It does not matter if you trade the Roggenrola or Boldore, both get a candy-free Boldore -> Gigalith evolve.
A list of the current Pokemon that have this free evolve after a trade are:
- Kadabra
- Machoke
- Haunter
- Graveler
- Boldore
- Gurdurr
- Shelmet
- Karrablast