Question

How do I get mareep to learn electric terrain from magneton?

Answer 1

To learn Mareep Electric Terrain you need to breed it with a Manectric, Luxray, Helioptile or Smeargle who knows the move. Magneton is genderless and thus can't pass on moves.

Comments

so I need to trade a Smeargle up in order to copy Electric Terrain from Magneton, then breed the Smeargle with the female Mareep?

Answer 2

You can't, magneton is genderless.
It can only breed with ditto.