There are many different ways to evolve the members of your team in the world of Pokémon. While the majority of species evolve by leveling up, there are a ton of other ways to get the job done, as well. Everything from turning your console upside-down to spinning in a circle has been used as an evolution mechanic.

One of the more common methods of evolution is via trade. Some Pokémon instantly evolve when traded to another person. Some of them need to be holding a certain item, while others do not. Here are some of the most interesting cases of trade evolution, and how they occur.

10 Feebas

Feebas is an interesting case in the world of Pokémon evolution, being one of the only Pokémon to ever have its evolution method changed. In Generation III and IV, Feebas would evolve into Milotic when leveled up with a high enough Beauty stat. From Generation V onward, this was changed, as the Pokémon contest was removed from the series.

Now, Feebas evolves when traded while holding a Prism Scale. This evolution method is much easier in many cases but is interesting to remember this Pokémon’s roots.

9 Haunter

One of the original trade-based evolutions, Haunter will not evolve into Gengar until it is traded. This makes one of the best Pokémon in Generation I harder to obtain than many people would have liked in the early days of the series.

This evolution method is attached to a long-running joke about Pokémon Diamond and Pearl, which contains an in-game trade with a girl named Mindy who lives in Snowpoint City. She’ll ask the player for a Medicham and offer a Haunter, making many believe she’s basically about to give you a Gengar. Once you receive it, though, she’ll laugh at you and point out that it’s holding an Everstone, preventing it from evolving.

8 Clamperl

There are a lot of Pokémon that have some sort of branched evolution, including ‘mons like Eevee and Gloom. One of the most notable is the Clamperl family, which has two potential branches. Clamperl can evolve into Huntail or Gorebyss, depending on how it’s traded. A held Deep Sea Tooth will make Clamperl become Huntail, while a Deep Sea Scale will make Clamperl evolve into a Gorebyss.

This is actually the only branched evolution that requires a held item for both branches, which definitely sets it apart from the rest.

7 Poliwhirl

When Generation II was released, it brought with it a series of what fans call “legacy” evolutions — new members of evolutionary families that were already established in an earlier generation. Pokémon like Chansey, Eevee, and Magmar have all received new evolutions in later generations.

One of the most interesting is the Poliwag family. Initially, Poliwag would evolve into Poliwhirl, which would then evolve into Poliwrath. These three Pokémon were all very similar, being basically blue circle with swirls on them. Poliwhirl’s new evolution, Politoed, is very different from the rest. It can be obtained by trading a Poliwhirl that holds a King’s Rock.

6 Kadabra

Like Haunter evolving into Gengar, Kadabra also represents a way in which super-powerful Pokémon in the first generation were locked behind alternate evolution methods. Abra, Kadabra, and Alakazam are all members of the powerful Psychic-type evolutionary family that is widely known to be one of the best in the series.

Kadabra will not evolve into Alakazam unless it is traded, though, meaning you’ll have to find a friend to trade with if you want to get your hands on this intimidating Pokémon. Also, their names are puns, which is fun.

5 Scyther

Some Pokémon that received legacy evolutions really didn’t need them, being either competitively viable or at least cool on their own. One example of this is Scyther, who was a widely-used Pokémon competitively and loved by fans. However, it was soon able to evolve when Scizor was introduced in Generation II.

Scizor was one of the first Steel-type Pokémon to be introduced when the type itself was brought in at the time of Generation II. You can obtain one by trading a Scyther that is holding a Metal Coat.

4 Graveler

Graveler is a strange case in terms of evolution. Geodude starts with two arms. Graveler has four, implying that Geodude sprouts two more for some type of evolutionary advantage. But then, when Graveler is traded, it evolves into Golem, which again only has two arms. Why does it lose two of them?

The case remains true for the Alolan variants of this line as well. However, Golem sprouts a glorious mustache after evolving. Where these two arms go upon evolution remains a mystery, but some fans have a theory.

3 Machoke

That theory is based on Machamp, another trade evolution. Machop will evolve into Machoke before Machoke becomes Machamp upon evolution. The theory goes that Machoke effectively “steals” Graveler’s extra arms because Machoke only has two while Machamp has four.

Whether or not this theory is correct, we may never know, but it definitely seems to make at least some sense. Some have also pointed out that Machoke and Machop have clear reptilian features, but Machamp does not. However, who does? That’s right — Golem. Spooky.

2 Porygon

Here is another unique case of trade evolution record-holding. The Porygon is the only time a Pokémon evolves by holding an item and being traded, and then evolves via that method a second time. Porygon will evolve into Porygon2 when traded while holding an Upgrade. From there, Porygon2 will evolve into Porygon-Z if traded while holding a Dubious Disc.

Apparently, the makers of Porygon tried to push its computing system even further, but it became corrupted, and thus the volatile Porygon-Z was born. Since it can apparently be pushed to evolve, maybe Porygon will one day become the first four-stage evolutionary line (outside of Mega Evolutions, of course).

1 Shelmet and Karrablast

Here is the most interesting trade evolution of them all — Karrablast and Shelmet. Not only do these two only evolve by trading, but they only evolve if traded for each other. No other combination of Pokémon will trigger either of their evolutions (including trading two Shelmet or two Karrablast).

The lore here is that Karrablast will “steal” Shelmet’s armor, becoming the newly-armored Escavalier. Shelmet will then live on without armor as the more vulnerable (and visually jaded) Accelgor. It’s a fascinating evolution method, albeit a bit of a pain, but unique nonetheless.

NEXT: 10 Gen 5 Pokémon That Should Get Galarian Forms