Answer: NIGHTSHADE
Explanation: Night Shade used to affect Normal-types back in Red, Blue and Yellow due to its always-doing-the-same-damage-irrelevant-of-types nature, but it doesn't affect them anymore in any of the succeeding games. The Gastly part is obviously there because Gastly learns Night Shade.
Answer: THICKCLUB
Explanation: The ghost refers to Marowak, not a Ghost-type - the hint is that "ghost" does not have a capital G. Marowak is practically never used in competitive battling unless it is holding a Thick Club, which doubles its Attack, but with it, it can be a force to be reckoned with, especially if it gets some help with Speed.
Answer: MEW
Explanation: Mew was thought unobtainable (without a Gameshark or Nintendo event) until the Mew Trick was discovered; however, it is still questionable whether it can really be counted as any more 'obtainable' than just with a Gameshark if it's only obtainable through a glitch.
Answer: LINOONE
Explanation: A LINE is generally straight, so one would expect that a Pokémon whose name comes from the word would be long and straight; however, as especially shown in its Ruby/Sapphire sprite, Linoone is all but stiff and straight.
Answer: HYPNO
Explanation: The nose on Hypno's Green version sprite looks a great deal more human than the nose looks in any of its successors.
Answer: LAIRON
Explanation: Many people who criticize the third Pokémon generation complain that many of the Pokémon are 'rip-offs' of older Pokémon. Lairon is one of the most frequently cited example due to its resemblance to Rhyhorn.
Answer: SKARMORY
Explanation: Skarmory is owned by Gonzap (the Colosseum main character's former boss), Winona (who is the answer to 18 across) and Steven (who is helpful to you on your journey through Hoenn, and also the Champion of the Pokémon League in Ruby and Sapphire).
Answer: WINONA
Explanation: Obviously, you have to figure out 16 across first and know that Winona has a Skarmory.
Answer: MACHOP
Explanation: Machop's Green version sprite is in the same pose as the FR/LG sprite, but in Green, one of its arms is undersized and the other is oversized. Machop's Pokédex entries all agree that it is bizarrely powerful, but the undersized arm does not look particularly so.
Answer: LUSTERPURGE
Explanation: Well... it's lust.
Answer: BLASTOISE
Explanation: Wartortle (29 across) evolves into Blastoise.
Answer: WEEDLE
Explanation: Weedle is drawn as brown and pink today, but it used to be yellow and red. Weedle is yellow when shiny.
Answer: ONIX
Explanation: Onix is only found on one floor of Rock Tunnel in Yellow. (It is found in other places, but not on any other floors in Rock Tunnel.)
Answer: WARTORTLE
Explanation: Wartortle evolves into Blastoise (24 across).
Answer: NINETALES
Explanation: Ninetales is often misspelled as "Ninetails". Since the misspelling turns the "tales" part into "tails", it sounds like the Sonic character Tails, especially considering that they are both multiple-tailed foxes.
Answer: ERIKA
Explanation: The animé episode in which Erika was featured was called "Pokémon Scent-sation". Obviously, this stems from "Pokémon Sensation", but is changed to a pun as the animé dubbers like to do. Therefore, it's not a Pokémon sensation anymore.
Answer: SANDTOMB
Explanation: Trapinch learns both Bite and Faint Attack, but not only does it have horrible Special Attack and great Attack, but it is also a Ground-type. The first actual Ground attack it learns is Sand Tomb, but its base damage is only a rather useless 15.
Answer: NATU
Explanation: Natu's Japanese name is Neitei, and the Icelandic word for no is "nei". I did not expect you to know that; however, words like 'yes' and 'no' in just about every language in existence are never more than a quick Google search away, and Icelandic is no exception. Both Natu and Xatu's names have four letters and start in "Nei" in Japanese (Xatu being Neiteio), but only in Natu's name is the "Nei" part exactly half of the name.
Answer: TAUNT
Explanation: When using Taunt in Ruby and Sapphire, a little hand appears and it waves a finger at the opponent.
Answer: POKEBLOCK
Explanation: "Their case" refers to the Pokéblock Case, which has many colors in it.
Answer: PHANPY
Explanation: Obviously, all Pokémon hatch from eggs in the games, and a Phanpy is shown hatching from an egg in an episode of the animé. Phanpy is nonetheless clearly based on an elephant, and elephants give live birth.
Answer: NIDOKING
Explanation: In FireRed and LeafGreen, Nidoking is one of a few Pokémon that can learn Megahorn. Megahorn is Heracross's signature move.
Answer: GOLEM
Explanation: The three Regis, Regirock, Regice and Registeel, are believed to be based on golems.
Answer: BELLYDRUM
Explanation: The most important role of Charizard in competitive battling is as a Belly Drummer. However, it is always a risky strategy because Charizard's defenses are not very good and Belly Drum takes away half of the user's Hit Points.
Answer: WHISCASH
Explanation: The Whiscash episode was banned for involving earthquakes, because when it was supposed to air there had just been powerful earthquakes in Japan.
Answer: SABLEYE
Explanation: When a Sableye faints in Pokémon Colosseum and Pokémon XD, the last thing it does in its fainting animation is to suddenly grin widely as the Pokéball absorbs it.
Answer: SPOINK
Explanation: According to the Pokédex, bouncing is what drives Spoink's heart, and thus, if it ever stops bouncing, its heart will stop and it will die. Logically, a paralyzed Pokémon will probably have a hard time bouncing.
Answer: OCTILLERY
Explanation: "Octo" means eight, and that is logical considering that after all it's based on an animal with eight limbs, but Octillery does not appear to have eight limbs in official art and game sprites.
Answer: ABSOL
Explanation: Absol learns Razor Wind naturally and can learn the Aerial Ace TM.
Answer: MILOTIC
Explanation: In order go obtain a Milotic (other than trading for one), you will first need to own a Feebas, which is quite a feat, because it only appears in six tiles on all of Route 119. Even after you've got the Feebas, though, you still need to evolve it, and to do that you need to max out the Feebas' Beauty and level it up by one level.
Answer: HITMONCHAN
Explanation: In Red, Blue and Yellow, when there were no genders, many people thought Hitmonchan was a female counterpart of Hitmonlee and was wearing a dress. When it turned out to be not only all-female but in fact all-male, many people were surprised.
Answer: UNIONCAVE
Explanation: You will have encountered a couple of caves before in the game, but Union Cave is the first you have to go through to complete the game.
Answer: WRAP
Explanation: In Red, Blue and Yellow, a fast Pokémon with Wrap had basically won the battle unless it missed or ran out of Power Points. However, in G/S/C onwards, Wrap is one of the least powerful and useful attacks in the whole game.
Answer: ENTEI
Explanation: There are no Johto legendaries to be found in Ruby and Sapphire. The first game to make the "unobtainables" obtainable was Colosseum, and the first legendary that the player encountered in it and could catch was Dakim's Entei.
Answer: ARBOK
Explanation: Jessie's Arbok in the animé always said its name as "Chaaaabok!" instead of "Arbok". I always found it kind of funny.
Answer: WILL
Explanation: 1337 is an Internet language, yes, but what it is supposed to stand for is "leet", which is a variation of "elite". Y2K obviously stands for the year 2000, which is the year that Gold and Silver came out. Will was a member of the Elite Four in G/S/C.