The breeding mechanic was first included in Pokémon Gold & Silver and has gone on to feature in every game since. Over the years, the mechanic has evolved to allow for some rather peculiar pairings. Unfortunately, it's not quite as simple as putting two random Pokémon together and letting nature take its course. If the right conditions are met though, a surprising amount of Pokémon species can be bred together.
First and foremost, the Pokémon need to be male and female. Anybody wanting to breed one of the series' numerous genderless Pokémon can get around this by putting them in daycare with a Ditto – although rather bizarrely – it's not possible for two Ditto's to breed. Next, the Pokémon need to share a common egg group. This is usually determined by the Pokémon's type, meaning that they can belong to several different groups. Once a suitable pairing has been made, it's just a case of waiting for nature to take its course.
Although in the games the species of the egg is decided by the female, thanks to this brilliant Pokémon Fusion Generator, it's possible to get an idea of what the offspring of these cross-species combinations might look like if Pokémon hybrids were a thing. Some of them might make for some interesting Pokémon, although most are abominations that not even Darwin himself could explain.
10 Tyranitar & Cubone (Monster)
The Monster egg group is pretty broad, allowing for quite a lot of strange combinations. Perhaps one of the most bizarre is Tyranitar and Cubone. Bizarre as it may be though, their offspring would be incredibly difficult to defeat in combat.
Given how powerful Tyranitars are already, the thought of encasing one in a protective layer of bone is really quite frightening. Tyranibone/Curanitar would be almost unstoppable and capable of dishing out and withstanding huge amounts of damage.
9 Blastoise & Stunfisk (Water)
Due to the wide array of Water-type Pokemon, there are actually three different Water egg groups. Both Blastoise and Stunfisk belong to the first, meaning that they could technically be bred together. Why anybody would be inclined to do such a thing is a bit of a mystery, but the option is certainly there.
The combination of Electric, Ground, and Water elements would actually make Blasfisk/Stuntoise a fairly formidable foe. Perhaps its strongest ability though would be its ridiculous appearance. Enemies would be far too busy laughing to be able to focus on the match at hand allowing Stuntoise to end things before the opposition even knows what's hit them.
8 Heracross & Dewpider (Bug)
The Bug egg group features plenty of powerful Pokémon, but it's hard to look much further than Heracross when looking for the strongest. There are 85 different Pokémon with which a Heracross could breed, but one of the weirdest has to be Gen 7's Dewpider.
Although the resulting Dewcross/Herapider may look strange, its ability to utilize Water, Bug, and Fighting moves would make it a fearsome fighter. It could hold its own in almost any match although would be easily beaten by any half-decent Flying-type Pokémon.
7 Sirfetch'd & Toucannon (Flying)
There are 63 Pokémon in the Flying egg group, although sadly, they're all fairly underwhelming. Many of the best Flying-type Pokémon either cannot breed or feature in different egg groups, meaning that finding powerful Pokémon in this group is somewhat difficult. Finding cool Pokémon, on the other hand, is much easier.
Sirfetch'd and Toucannon are two of the coolest looking Pokémon out there and can breed if placed in daycare together. The Toufetch'd/Sircannon that doing so would yield is every bit as cool as its parents. It wouldn't be a particularly strong Pokémon but it would probably do quite well if entered into one of the game's Pokémon contests. Getting hold of a Sirfetch'd might not be that easy though.
6 Nidoqueen & Wailord (Field)
The Field egg group contains more Pokémon than any other group. This means that there are theoretically thousands of different breeding combinations available. Interestingly though, it's not possible to breed a Nidoqueen with a Nidoking to create little Nidoprinces and princesses. It is however possible to breed a Nidoqueen (and just about any other Pokémon from this egg group) with a Wailord. Pokéscience is strange.
Nidolord/Wailqueen is one of the derpiest looking combinations out there. Despite it having a face that only a mother could love, it would likely be a fairly strong hybrid. With resistance to seven different types, most Pokémon would struggle to deal any noticeable damage to it. Its huge strength and size would make it just as troublesome offensively too.
5 Jigglypuff & Pikachu (Fairy)
As Pikachu and Jigglypuff both belong to the Fairy egg group, it's possible to breed them together. There are plenty of other combinations available in this group, although this one seems quite fitting given that the pair both appeared in Super Smash Bros. back in the late '90s.
Jigglychu/Pikapuff is one of the cutest Pokémon hybrids and would likely fare pretty well in battles. It might not have much in the way of physical strength or defense, but that doesn't mean it couldn't pack a punch. Pikachu's ability to shock the opposition combined with Jigglypuff's singing skills would make for a deadly combination.
4 Golurk & Cofagrigus (Mineral)
The Mineral egg group typically includes Rock, Ground, Ghost, and Steel-type Pokémon. As a result, there are a fair amount of Pokémon to choose from. One of the strangest pairings though has to be Golurk and Cofagrigus.
As if four weren't already enough, the resulting Cofurk/Golagrigus would have a rather ridiculous eight arms. Whether or not this would make it an arachnid and thus also a Bug-type Pokemon is up for debate. Regardless, though, it could certainly dish out some serious punishment. Or cuddles, if its trainer is feeling down.
3 Muk & Gardevoir (Amorphous)
The Amorphous egg group features some of the series' more bizarrely designed Pokémon. Muk probably tops that list on account of it being a living pile of sludge. With that in mind, it seems only right to pair it with one of the more normal-looking amorphic Pokémon.
Garduk/Mukevoir may look a lot like a failed science experiment. However, the combination of Psychic, Fairy, and Poison would give it a real edge in battle and its viscous consistency would allow it to absorb massive amounts of damage. Just don't try entering it into any beauty pageants though, as it's unlikely to bring home any ribbons.
2 Electabuzz & Magmar (Human-Like)
The Human-Like egg group is one of the strangest to feature in the game, especially considering how unhuman-like most of its Pokémon are. Electabuzz and Magmar were two of Gen 1's most underrated Pokémon but could combine to create an almost unstoppable hybrid.
Magmabuzz/Electamar would be deadly against pretty much every type apart from Ground. With access to powerful moves like Thunder, Hyper Beam, and Fire Blast – its damage output would be off the chart while its intimidating appearance would have many of the series' smaller Pokémon too terrified to move.
1 Charizard & Magikarp (Dragon)
The brilliantly designed Charizard and the potential powerhouse that is Magikarp both belong to the Dragon egg group. As such, they can technically breed. Exactly how this process would work is something of a mystery.
As intriguing as the idea of a flying fish that can breathe fire is though, the resulting Charikarp/Magizard really is the stuff of nightmares. As such, it's probably for the best that they're not included in the series. On the plus side, burning it with fire is certainly a valid option thanks to Charizard.