Pokemon that could only be obtained by trading were difficult to get. Pokemon that could only be obtained by trading when they had the correct item were even more difficult to get. Even now, with the addition of the GTS and Wonder Trade, these Pokemon can still be tough to get. On the GTS, someone may offer one of these Pokemon and maybe even give it the correct item if needed but they will usually ask for a Pokemon that is nearly impossible to get. You may have more luck with Wonder Trade, but you need luck to get the correct Pokemon. Luckily, not all of these Pokemon have to be obtained using this method. In generation six, the Stump Pokemon Phantump can only evolve when traded, but its evolution can be found on Route 20. Trevenant, the Elder Tree Pokemon, along with its pre-evolution, are Ghost/Grass types. But should you get a Phantump?
If you don’t have a Grass type at this point in the game, getting a Phantump might be a good idea. Just remember that unless you have a good enough friend who will trade you your Pokemon back, it will stay a Phantump. You could always try to get one on the GTS, or try your luck with Wonder Trade. Unless you really need one to fight Olympia or something, I highly suggest you get a Trevenant instead. Even then, its abilities aren’t all that great. Frisk is more useful for finding items and Natural Cure is only useful if your opponent gave you a status condition. Its hidden ability, which is possible to get through hordes, can be useful if you have a Pokemon that can cause harsh sunlight. Even if you don’t, it’s still a useful ability. I would suggest giving your Harvest Trevenant a Sitrus Berry so it can possibly keep recovering health. Without sunlight, it has about a 50% chance of getting a new Sitrus Berry after it uses it, while it has a 100% chance to do this in sunlight.