While catching them all is the tagline for the Pokémon series, it's a lot harder than it seems. Sure, you won't have a hard time evolving your starter and getting your standard Pidgeys and Rattatas, but the easy road ends there. As you continue your journey, you realize that there are fossil creatures to catch and numerous legendaries to discover, and that's without taking into account the already hard-to-find Pokémon.

The point is that finding every single Pokémon is hard work, and it takes pure dedication in order to accomplish this task. The problem becomes even more frustrating when you start to determine some of the catch rates for specific creatures and find out that some are version exclusive. It's almost as if Game Freak doesn't want you to find all of the creatures in their games.

However, we're not taking a look at catching them all. Instead, we're looking at the Pokémon that are so hard to find you'll be gripping your sweaty 3DS into the late hours of the night. These creatures are so tough to come by that few have ever stuck it out to succeed. Even I haven't captured all of them myself, but I do know how to get them.

For those of you hardcore players out there, here is a comprehensive guide of the 20 rarest Pokémon (in no particular order) and how to catch them.

20 Mareanie

Toxapex is one of the best Pokémon in the Sun and Moon metagame. However, it is impossible to find one in the wild. Instead, you have to look for its pre-evolved form, Mareanie. Unfortunately, Mareanie is still not an easy catch and requires some patience, along with a special item.

The first thing you have to do is find a Corsola in the wild (which already has a low spawn rate). Then, you have to use an Adrenaline Orb to persuade it to call a partner into battle. From there, you simply cross your fingers and hope that it summons a Mareanie into the fray, but odds are that you'll be waiting quite a long time. There is no way to capture this Pokémon unless you trade.

19 Celebi

There are some Pokémon that are just hard to find in general. Then there are others that are so ridiculously rare that you cannot acquire them through normal means. Celebi is one of these creatures. At the time of this writing, there is no legitimate way to get Celebi without using some sort of event or hacking the game.

There have been a few times Nintendo held an event where you could get one, though. There was one done for HeartGold and SoulSilver that then triggered a special event in the game. There was another done for the 20th Anniversary of Pokémon itself. Needless to say, there are a lot of Celebi floating around. If you know what to trade, then you won't have any trouble getting one for yourself.

18 Munchlax

In Generation Four, Game Freak gave a lot of existing Pokémon either a baby evolution or extra evolution. In the case of Snorlax, a baby Pokémon was given in the form of Munchlax. You would think that to get one, you would simply stick a Snorlax in the daycare with a Ditto and you're home free, right? Wrong.

Munchlax, in my opinion, is one of the most needlessly complicated Pokémon to capture. When introduced in Diamond and Pearl, Munchlax was instead linked to the trees that players can cover in honey to attract Pokémon. The game assigns 4 out of 21 trees to spawn a Munchlax through this process (and they are random). If you manage to find one that has a Munchlax, you'll then deal with a spawn rate of 1%. Grind away.

17 Manaphy

Another Pokémon on the same level as Mew and Celebi, Manaphy was introduced in Generation Four. However, unlike some of the other special Pokémon, there was a legitimate way to acquire a Manaphy. And, believe it or not, it's a method that still works today, if you have the old hardware and software to support it.

If you were hardcore enough to also have a copy of Pokémon Ranger, you could eventually come across the Manaphy Egg. Once you get it, you can then transfer it over to your copy of Diamond and Pearl, where it will eventually hatch into a beautiful Manaphy. However, don't attempt trying to hatch a Shiny one. That won't work unless you receive the Manaphy Egg from another trainer entirely.

16 Feebas

Anyone who played Ruby and Sapphire will tell you how brutally annoying it was to find a Feebas in the wild. These fish were so tricky to discover that players spent days looking for just one. What made this more frustrating was that its evolution, Milotic, was an extremely useful Pokémon in battle.

Why is Feebas so difficult to find? Well, there's only one route where it can be caught. However, you can't just fish anywhere in the water and wait for one to nibble. Instead, there are specific water tiles that the game selects at random to hold a Feebas. Then you must deal with a catch rate of only 1% while you wait for this elusive fish to show up. Let's hope that getting your beautiful Milotic or filling your Pokédex is worth the effort.

15 Phione

Another pretty rare Pokémon to find is Phione. Right off the bat, you'll notice that it looks very similar to Manaphy. While their relationship has yet to be properly explored, it's clear that the two have some kind of connection. Even though it made this list, there are two legitimate ways to get a Phione for your roster.

The first of these ways is through My Pokémon Ranch. If you send over 250 Pokémon from Diamond and Pearl, then the ranch owner will offer you a trade for a Phione. However, if My Pokémon Ranch isn't your thing, then you can make good use of that Manaphy from Pokémon Ranger. Simply put in the daycare and breed it. You'll then get an egg that will hatch into an adorable Phione.

14 Spiky-Eared Pichu

Here is one of the more interesting events in HeartGold and SoulSilver. Nintendo ran an event where you could go to GameStop and download a special Pikachu-colored Pichu (which was just a fancy way of saying that it was shiny). Once this Pichu made it into the game, it triggered an event in Ilex Forest.

Travel there with your special Pichu and you'll encounter another Pichu with a spiky ear. After playing around with it for a hot minute, it will join your roster. It comes with unique moves that Pichu can't normally learn, so that's pretty exciting. Unfortunately, this Pichu cannot evolve or be traded to other games, so it's stuck in HeartGold and SoulSilver. This is why the Spiky-Eared Pichu is so rare.

13 Jirachi

Jirachi is the special mythical from Generation Three. Being a Psychic and Steel type, it was quite a headturner when it was released. Unfortunately, it's pretty difficult to come by and one of the rarest Pokémon ever created, even more so than Mew.

There were a few times where Nintendo released events where you could download a Jirachi into your game, but the most notable one was with Pokémon Colosseum on the GameCube. Some copies of the game came with a bonus even disc that allowed players to receive Jirachi within the game. It was extremely powerful and proved to be useful when grinding through the Battle Tower. Other than that, there aren't any legitimate ways to get this little guy.

12 Salazzle

Many people got wind of Salazzle coming to Sun and Moon and immediately wanted it. After all, a Poison and Fire Pokémon that could poison any other type in the game is an opportunity to amazing to pass up. Little did they know (myself included) that it would be very difficult to capture a Salazzle.

While it's not hard to find a Salandit, only the females can evolve into Salazzle. The males just stay Salandit for the rest of their lives. This would be fine if female Salandit didn't appear a mere fraction of the time that male ones did. This led to a lot of frustrated trainers as they leveled their Salandit past its thirties, only to find that they had the wrong gender from the very start. This has made Salazzle a must-have for anybody doing extreme trading.

11 Victini

Victini is an adorable little Pokémon, but like Mew and Jirachi that came before it, that means that it will be incredibly difficult to find. Through legitimate means, Victini can only be obtained in Black and White through a Wi-Fi event. Unfortunately, that event only took place during the game's launch window and has since been long gone.

Players who had the game could download an item known as the Liberty Pass. This allowed trainers to enter Castelia City and travel to a place called Liberty Island. After they battled through a few Team Plasma grunts, Victini would be at the very end and ripe for the taking. There have been a few other events to bring this Pokémon to players across the world, but none going on currently.

10 Shiny Vespiquen

Shiny Vespiquen has been renowned as one of the most sought after Pokémon in existence and needs to be discussed here. In this case, it brings about the same difficulties as Salazzle.

As you can already guess, not every Combee can evolve into a Vespiquen. For that, you need to find a female. However, if you thought finding a female Salandit was hard, you haven't seen anything yet. The odds of finding a female Combee are even less, so you'll be hunting for an even longer time. Then add on top of that the chances of finding a Shiny Pokémon. I bet that you'll probably hunt for about a week before you get sick of it and move on to more fun games.

9 Mew

Ever since Pokémon Red and Blue hit the GameBoy, Mew has been one of the rarest Pokémon to come by. As a matter of fact, there were many rumors floating as to how you could actually capture one. Eventually, it was discovered that many of them were false and the only way to find a Mew was to glitch the games.

Mew was added into the entries fairly late in development and was never included as a Pokémon you could encounter. Nonetheless, there is a complicated exploit that can cause you to find one in the wild. It takes some serious glitch work, including screwing with some battle sequences. I can't go into much detail here, but there are plenty of YouTube videos on the subject. If you placed 1,000 Pokémon into My Pokémon Ranch though, thatś another way of getting a Mew.

8 Wimpod

Wimpod is one of the most aggravating Pokémon to capture and that's for multiple reasons. The first is that Wimpod are pretty difficult to battle in the first place. I'm not saying that they're powerful. I'm saying that simply getting one to fight you is a major pain. You'll find them scuttling along the beaches of Alola in the overworld. You have to run up and catch one in order for it to fight you. If they get away, you have to wait a full 24 hours before trying again.

Then to make matters worse, if you manage to battle one, you have to be extremely careful. If you knock its HP down below 50%, it will immediately run away. This means that most people will have a rough time nabbing one during a real playthrough. Wimpod are not a fun time.

7 Shaymin

For some reason, Generation Four had a lot of event mythicals and Shaymin is another one of these difficult to find Pokémon. There are a few legitimate ways to capture one, but without a good trade or a decent Action Replay, you're going to have a hard time getting one for yourself.

When it was first introduced, Shaymin was put into Diamond and Pearl alongside an event that gave players access to an item called Oak's Letter. You use this to meet Professor Oak and he will let you go on a completely new route (that you can't travel on otherwise). Simply follow the road to its very end and you will meet Shaymin there. This event would later reoccur in Pokémon Platinum. If you Action Replay it, though, you can simply run through walls and get there.

6 Dhelmise

In a Pokémon game based on a tropical setting, I suppose it makes sense that there would be a creature modeled after an anchor. Luckily, it turned out to not be dumb like Vanilluxe or Klefki. Dhelmise is essentially a haunted anchor and takes the Grass-Ghost typing. However, in order to find it, you have to fish in a very particular area. That premise alone is worth the trouble.

If you've played through Sun and Moon, you'll likely remember the boat that looks like a Steelix. If you enter it and go all the way to the end, you will encounter a man who is fishing in a small space. Cast your rod and have tons of patience. Dhelmise will eventually appear, but its spawn rate is so low that you won't see it for quite some time.

5 Darkrai

Darkrai is the third event mythical from Generation Four on this list. Much like Shaymin, Darkrai can only be accessed through an event that is identical in both Diamond and Pearl and Platinum. 

In order to get Darkrai, you need an item called the Membership Pass, that allows you to stay at a special hotel in Canalave City. Once you go to sleep, youĺl get a nightmare of your own and wake up on New Moon Island (just a few clicks away from where you find Cresselia). If you travel to the heart of the island, you will encounter the nightmarish Darkrai. Without access to other events, there is no way to obtain this Pokémon unless you know how to make a good trade with other trainers online.

4 Togetic

Togetic was introduced in Generation Two along with Togepi and isn't very difficult to obtain within the games. Fast forward a few years to the Gen 2 update on Pokémon GO and a much different story is told.

While you could originally obtain it only by evolving a Togepi after getting so many out of an egg (which is a pain), it was eventually made available to find in the wild. That said, Togetic remains one of the toughest Pokémon to catch in the game. Not only is it already difficult to find, but it's difficult to snag. Togetic's catch rate is so low that players have rushed through their Ultra Ball stockpile just trying to acquire one of these little buggers. Unfortunately, Togetic remains as frustrating as ever. It can be caught with less aggravation nowadays, but it's still not easy.

3 Specific Shiny Spinda

Spinda is one of the most unique Pokémon ever created. While there isn't anything unique about its capability in battle, Spinda has an interesting gimmick. Each Spinda you find will have a different layout of spots. However, the number of layouts isn't unlimited. There are only millions of options to find, making it nearly impossible to come across the same pattern twice.

Combine this with the likelihood of finding a Shiny Pokémon and you're bound to be hunting for the rest of your life. Finding a Shiny Spinda in and of itself isn't too bad, but if you want one with a specific pattern, I guarantee it'll be the last thing you do. That having been said, I'm not sure why people would be so intent on getting a shiny variant of that one Spinda pattern.

2 Wish Chansey

Of all of the rare Pokémon ever introduced in the series, none have become more desired or famous than Wish Chansey. This is a Chansey that has the move Wish (it cannot learn that move through normal means in the game). You see, back when FireRed and LeafGreen were big, Nintendo held an event that gave a lot of classic Pokémon the move Wish. Chansey was one of the ones on the list.

Unfortunately, due to the nature of the event, there are only a handful of people who received the Pokémon. That's not to say it's impossible to get one, but it's extremely difficult. Since breeding those Chanseys won't get you more Wish Chansey's, there are a finite number of them out there. If you find yourself lucky enough to get one, make sure that it's not some kind of hack first.

1 Shiny Legendaries

As if Legendary Pokémon weren't difficult enough to find on their own, it becomes even more challenging when you through the Shiny variant into the mix. Believe it or not, getting a Shiny Legendary Pokémon is possible, but it's one of the most frustrating and tough processes you'll ever go through.

The only way to do it is by finding a Legendary you can encounter in the overworld. After you select it, the battle triggers. However, if you save it and keep retriggering the battle, there is a chance that the Pokémon in question will appear as Shiny. What makes finding a Shiny Legendary even more challenging is the fact that some of them are impossible to obtain. Keep your eyes peeled when you look for those special Legendaries.