Nidoran in Kanto - To be honest, I don't know why they never gave Ash a Nidoran, maybe because is was a 'weak' trainer in Kanto. It would have be a nice rivalry for Ash and Gary, but in the end, Gary caught both Nidoqueen and Nidoking.
A Hitmon in Johto or Kanto - Honestly, I think Ash should have caught one of these pokemon. I don't really have a reason for this one, I just thought it would be a nice pokemon for him to have.
Sentret in Johto - At the time, it was out first taste of new pokemon. Sentret was the first brand new pokemon we ever saw when we first got Gold and Silver. I think Ash should have caught one. At the time I thought Sentret was just so awesome and I think it would have been amazing for Ash to have got one, but instead, he catered to his older pokemon and all the starters.
Flygon in Hoenn - Not only one of the most popular Hoenn Pokemon, Ash also teamed up with one like it was his on in the Jirachi movie. When I saw this movie and I still wish it today, I really want Ash to catch one. It is by far probably one of the most popular pokemon, but it doesn't get much love in the anime.
Floatzel in Sinnoh - Just wish Buizel had evolved. Why they made the choice not to is beyond me. Especially after Corphish didn't evolve.
Stunky in Sinnoh - Honestly, this is just another one of those pokemon where I thought Ash would have caught one, but he didn't. This was probably because Officer Jenny used them in Sinnoh in a lot of episodes and the fact that it was a skunk, which is not an animal people tend to like.
Gabite - I think Gible should have evolved at least once. Didn't have to evolve all the way, but it would have been nice if Gible had evolve once it mastered Draco Meteor. Or evolved to master it.
Hippopotas in Sinnoh - out of every pokemon Ash has encountered, this one is probably the most disappointing that he didn't catch. This pokemon showed up in a few episodes, always falling on Ash's head. They also just seemed to really match each other. I had always hopped that Ash would eventually catch this pokemon, but he never did. I think they were eventually going to do something similar to how they handled Sandile, but in the end, gave Ash Gible.
Emboar in Unova - Honestly... why the hell did they stop Tepig from going all the way to Emboar? Pignite is probably the most hated out of all the Unova Starters, yet they just stop... Pignite was beyond powerful and a lot like Charmander in many ways. I just really think it was terrible writing to stop him at Pignite. Bianca having an Emboar shouldn't have stopped it from evolving. I mean Paul and Ash both had a Torterra.
Dewott in Unova - I understand that Oshawott was a market pokemon, but I think Dewott would have just been as good. I don't think it would even need to change its personality. It could have kept it in evolution.
Venipede in Unova - Again, this is another one of those dang pokemon that Ash bonded well with, but didn't catch. Honestly, I think they were eventually planning to let him catch it, but when the Plasma vs Rocket episodes were canceled, I think they had to change a ton of stuff.
Solosis in Unova - Just another pokemon I wish he had caught. Probably by far my favorite Psychic type ever, but not even sure if the pokemon appeared.
Vanillite in Unova - I know this pokemon is probably one of the most hated among pokemon fans. And I really don't understand why especially if you compare it to the past pokemon. Anyway, I think if Ash had caught this pokemon, it would have made it a lot more popular. It has happened before and I think it would have happened again.
Braviary in Unova - Probably the most iconic pokemon for Unova, it being based on a Bald Eagle and they didn't let Ash catch it.... sigh..... So much disappointment when it came to pokemon in Unova.
Larvesta in Unova - I just think it would have been a better egg pokemon than the random ass Scraggy he got which got the most screen time, yet didn't evolve at all....
Litleo in Kalos - I honestly think this pokemon would have been great for him. He protected it and seemed like he was going to catch it.... but in the end.... it walked away.... I think Pyroar would have been a great rival for Luxray if it had appeared when it was supposed to have appeared.
Gogoat in Kalos - Honestly, I thought this was 100% given. How wrong we were.... first time ever he has never caught a grass type. When he got a Noivern, I thought a Skiddo was soon to follow. They didn't even mention the abandoned Skiddo in Lumiose City. Skiddo would have been a great pokemon for Ash.
Swirilix in Kalos - The only Fairy type I though Ash had a chance at catching... and it didn't happen thanks to an annoying trainer by the name of Sawyer...
Honedge in Kalos - Again... thanks a lot Sawyer... Would have been a great unique typing for Ash. Not to mention he had never caught a Steel or Ghost type pokemon other than Haunter who he got rid of.
Skrelp in Kalos - Much like Venipede, I think he should have caught a Skrelp after the 4th Gym. The main reason for this was probably because it was a water bound pokemon and there was little of that in Kalos after the first part.
