In Pokémon, the Pokédex is presented as a scientific encyclopedia full on information on the currently-known species. The information it presents regarding each Pokémon contains interesting factoids and statistics, but some entries are frankly ridiculous.
Professor Oak has clearly gleaned some knowledge from all his years studying Pokémon, but in many cases, it seems he has neglected other basic studies. From entries that ignore basic logic and scientific fact to Pokémon whose very way of life is absurd, here are some of the most ridiculous Pokédex entries of all time.
Spoink
Spoink is a rather cute Psychic-type introduced in Generation III. It's known as the Bounce Pokémon due to its amusing habit of bouncing everywhere on its coiled tail. However, this becomes less amusing when the player reads any of Spoink's Dex entries. Ruby reveals that the shock of bouncing allows Spoink's heart to pump blood around its body -- meaning, if it ever stops bouncing, it will die.
The life of a Spoink must be one of eternal anxiety. If one stops moving for even a second, it could drop dead, their Emerald Dex entry claiming they even continue to bounce in their sleep. The sheer absurdity of this creature is staggering. Despite this, Spoink is shown frequently in the anime staying still, which could either be an inconsistency or evidence that the Pokédex is sometimes wrong.
Primeape
Primeape takes us from a creature that will die if it ever calms down to one that will die if it doesn't. The Pig Monkey Pokémon is an iconic creature from the first generation that's remembered for its foul temper and short fuse. What is less commonly remembered is that, according to its Sun Dex entry, Primeape have been known to become so angry that they die.
The concept of a creature becoming so angry that it literally stops living is ridiculous. The latter half of the Sun entry also states (rather disturbingly), "Its face looks peaceful in death, however." Whoever wrote this entry thought it pressing to note the expression on Primeape's corpse. This also means that Primeape can only ever know peace in death, its only escape from its constant rage.
Darumaka
The Fire-type Darumaka is native to Unova, the Pokémon world's version of the United States' New York metropolitan area. However, the game takes some liberties in regards to terrain and climate, making part of Unova a desert, home to the Zen Charm Pokémon. This all makes the fact that Darumaka's White Dex entry says that people have been known to shove this Pokémon's droppings in their clothes to keep warm (somehow) even weirder. Perhaps it would be one thing if Darumaka was native to the snowy Sinnoh region and ancient people had no other option to survive, but it isn't. Also, the Pokédex never says how long ago this occurred, meaning it could have happened thousands of years ago or last Thursday.
Grimer
Grimer is the Pokémon series' equivalent of a JRPG's common slime enemy, but the origin of this creature is inconsistent to say the least. Gold's Dex entry states that, as a Grimer moves, pieces of it fall off and become new Grimer, while Sapphire claims that sludge from polluted seabeds eventually become Grimer. However, is Pokémon Stadium's Dex entry that truly takes the cake, calling Grimer "Sludge that was transformed when exposed to X-rays from the Moon."
This is ridiculous for several reasons. First, the Moon doesn't produce X-rays -- the Sun, stars and comets do. Clearly, Professor Oak is not an astronomer. Secondly, these explanations are so different that it's hard to determine which one (or ones) is true. Diamond and Pearl attempted to retcon Grimer's origin by explaining that polluted streams exposed to X-rays from the Moon produce Grimer, but this still runs into the issue of the Moon not producing X-rays.
Magcargo
Many of Magcargo's Pokédex entries mention a simple fact about it: its body temperature can reach 18,000 degrees Fahrenheit. To put that into perspective, the Sun is estimated to be just under 10,000 degrees Fahrenheit, meaning that the Pokédex claims a Magcargo is almost twice as hot as the sun. At that temperature, the world around Magcargo would combust. Its Poké Ball would explode, making owning one impossible, and standing too close to Magcargo would kill a trainer instantly.
Some have argued that this may only be Magcargo's internal temperature, meaning that it would not actually ignite people and places simply by existing. This is a fair argument, but that means that a Magcargo using Flamethrower would probably be letting loose 18,000 degrees of heat from inside its body -- which would definitely cause some problems.