As a big fan of Pokémon games, I recently tried to challenge myself by attempting to beat Pokémon Crystal by only using Rock Pokemon. My beefy-boys-only team of Graveler, Onix, Sudowoodo, and Shuckle were doing well for the first four gyms, but we ran into some trouble in the second half of Johto.

For most of the first half, these four Pokémon were either strong enough (Graveler’s Magnitude) or crafty enough (Shuckle’s Rollout), to make it to Olivine without any problems–but this is where Water Pokémon, my team’s greatest weakness, starts to come into play.

I started looking at other ways to bolster my team. Rhydon can learn Electric-type moves like Thunder by TM, but it’s not possible to catch a Rhydon until you reach Victory Road. Fossilized Pokémon like Kabutops, Omanyte, and Aerodactyl are not available until Cinnabar late in the game; Magcargo isn’t available until Kanto (and would have 4x weakness to Water anyway); and Tyranitar, the game’s pseudo-legendary dinosaur, isn’t available until Mt. Silver–the last location in the game.

My last remaining Rock-type option was Corsola, a dual Water/Rock-type Pokémon that you can fish out of Olivine City’s port waters, and to my surprise, the little coral buddy was able to solo the rest of the game at level 60 herself.

In all my years of Pokémon, I never once picked up a Corsola. How could I have known it had this potential? I remember doing things like running a Rhydon that knew Surf and Thunder as a sixth man-of-the-year Pokémon in earlier play-throughs as a kid, but it never dawned on me that Corsola could win the entire game on its own.

So how did I do it? Well, it didn’t matter that I was playing a Rock-type only challenge anymore, because after getting Corsola to level 37 it became clear that a Corsola-only challenge was not only more exciting, but it also seemed entirely possible.

Running Corsola with Surf, Recover, and Ancient Power meant that I had two powerful Special attacks for my Water/Rock typing, and a healing move to regain HP. Once it was leveled up high enough, its base-85 Special Defense stat kept it mostly alive, requiring two hits of a Water or Fighting rival to KO the coral cutie.

At level 37, however, Corsola learns a move called Mirror Coat–an extremely rare Psychic-type move that only three other Pokémon can learn in the entire game. The way Mirror Coat works is that if the opponent hits you with a special move, Mirror Coat will respond with twice as much damage dealt. Physical and Dark-type moves will cause Mirror Coat to fail, but otherwise, if you can survive the attack, it will deal twice as much damage back at your opponent.

Mirror Coat was introduced in this generation of Pokémon games as the signature move of Wobbuffet, an odd amorphous blob of a Pokémon that became popular thanks to the Pokémon anime series, where it was owned by one of the antagonists: Jessie of Team Rocket.

In the game, however, a player would have to go out of their way to catch a Wobbuffet, meaning that most people probably never even came across one. The only way to get a Wobbuffet was to travel to an area known as the Dark Cave at night and find one with a 10% appearance rate. This area was only accessible however after making it to Blackthorn City, the second-to-last location in the region before the Pokémon League.

The other two Pokémon who could learn Mirror Coat were Electrode (a weak Electric-type Pokémon, despite being one of the fastest in the game), and Suicune (a legendary Pokémon that learned it all the way at level 61).

Not only did Corsola learn Mirror Coat way earlier at level 37, but capturing one is also very simple. Fish at Olivine City with a Good Rod (given to you by a fisherman in that same town) and find one in the morning.

From then on out, I was able to counter back every powerful special move sent at me while alternating healing back up with Recover. For my opponents, it made coming up against Corsola like playing tennis against a wall.

It didn’t matter that Claire’s Kingdra was a powerful Water/Dragon-type because I sent every Surf back at double the force. At the Elite Four, Will’s Psychic-type Pokémon were hit with Psychic’s twice as powerful as the ones they sent to me, Bruno’s Pokémon went down to powerful Surfs, and Corsola was able to regenerate its own health. Against Lance, the Champion, every Hyper Beam was a godsend knowing Corsola could refract it back with double the power.

Corsola still retained its Grass and Fighting weaknesses, but there wasn’t any Grass Pokémon left to conquer, and when I challenged Erika later in the game, I momentarily switched out Surf for Ice Beam thanks to the Move Deleter, a handy TM, and the ability to relearn Surf. Most fighting moves also couldn’t KO Corsola with one-hit, but I gave the little buddy a Focus Band just in case, which is a held item that has a 12% chance to save your Pokémon from fainting and survive at 1 HP. In two separate occasions, it saved Corsola’s life: once against Erika, and the other against Bruno’s Machamp.

Corsola is apparently not the best Pokémon in competitive play since the format is double battles, but otherwise, Mirror Coat really is that move. In fact, Wobbuffet was even banned from most single-battle competitive tournaments altogether since it could learn Mirror Coat and Counter, as well as trap Pokemon from switching out.

At the end of the day, these games aren’t hard to beat–and there have been countless runs where competitive gamers have won with just a Weedle, etc.–but I honestly had a lot of fun discovering just how awesome a Pokemon Corsola was. It may not be just the most underrated Pokémon, but one of the best Pokémon ever created.

What do you think? Drop your thoughts in the comments below.