There's a lot of items that sit uselessly in your bag if you can't do a trade evolution. So I decided to turn them into competitively useful items instead of dead weight. Note that these were designed flavor first, power/utility second.
Currently, there's eight fully evolved pokemon with Terrain setting abilities, and four of those are legendaries. That leaves very few options if you want to actually use terrain, especially when one of them is Pincurchin. So let's open them up to new users.
Electivire - Since Electric Surge is only on a terrible pokemon, I think we can give it to one that's almost good already. I think the power boost of terrain can push Electivire past the limits of being a physical electric type and actually make him usable. It could easily replace Vital Spirit for cancelling out sleep. Also Iron Hands is one of the best Future Paradox mons, but having their terrain setter be a similar physical electric type could force some interesting teambuilding decisions.
Gogoat - Rillaboom gets to use Grassy Surge for the power boost, so I wanted to make the second setter a bulky boy to explicitly use its healing powers. Gogoat is a tank that hasn't yet been viable, so it feels alright to give it to him. Plus with his myriad methods of medication he could become a real drain-tank. The only minor problem is his natural EQ/Bulldoze coverage getting nerfed, but that might be a sacrifice he needs to make.
I've considered Meganium here in the past, but after it got Mega Sol that would become an absurd boost.
Orbeetle - Psychic Surge is the trickiest one to place, because it already has a whole archetype. I don't think it should be given to a pokemon who either learns Expanding Force or is a natural Trick Room user, which is why I chose Orbeetle. I'm not super happy with this choice since it was done by elimination, but maybe it'll give him a niche.
Alcremie - Misty Terrain is the only purely defensive terrain, so it should go on a more supportive pokemon. Alcremie already has a small niche with Decorate, but this could push it into a more solid spot in the metagame by protecting the sweeper it's trying to set up.