I'd remove the Spearow line's Normal type, so that way they're at least a little more memorable by not having that infuriatingly common Normal/Flying typing.
Aesthetically, you know what'd be cool? Spearow and Fearow look too much like generic birds, so I think giving them more interesting designs would do them justice. Fearow learns quite a few "drill" moves, so I think it'd be pretty cool if we made the Spearow line look like drills or other construction equipment. Give them some extra black-and-yellow plumage too, why not. They'd be great partner Pokémon for Workers!
I'd give the Spearow line Brave Bird because
for some reason they can't learn it. In line with how I'd redesign them, I'd also give Spearow Drill Run.
There's no reason for us to have
two early-game birds, so I'd make the Spearow line more late-game, and accordingly I'd buff their stats. Add some Attack, and especially some HP, since a lot of Fearow's dex entries say it has great stamina.
I'd change the Pidove line similarly. They're just unbelievably bland, aside from Unfezant having gender differences (and even female Unfezant looks terrible). I'd make them pure Flying-types too.
Design-wise, I'd change Tranquill to look a little more colorful, and give it some gender differences as well (maybe male Tranquill have brighter plumage?). I'd make male Unfezant more like a peafowl, with cooler, showier plumage, and I'd make female Unfezant plumper and more like a turkey.
I'd give male Unfezant the ability Intimidate, as well as buff its HP a bit, and I'd give female Unfezant a
lot more bulk in exchange for Attack and Speed. That way, we bascically have two unique Pokémon for the price of one!
Patrat and Watchog need some changes too, especially since Lillipup is another early-game Normal-type. Let's make them Normal/Psychic. Let's give them Psychic-type moves, better Special Attack, and Dazzling too, for the heck of it.
Something that's bothered me about Generation V's Pokémon is how strangely some types are represented. For example, all the (non-Legendary) Psychic-types are either pure Psychic or Psychic/Flying. So let's make the Elgyem line Ghost/Psychic. We kinda have too many pure Psychic-types as it stands.
Goldeen is...certainly a Pokémon. Why does it exist when we already have Magikarp as our ubiquitous Water-type? Goldeen evolves at a later level than Magikarp, and yet Seaking is still a terrible Pokémon; really the only thing it does to stand out is have Lightning Rod as an ability. Let's give Seaking a cooler horn and boost its Attack and Speed a bunch, why not. Let's give it Electric attacks too.
Bruxish is an often forgotten one, but I hate its design so much that that's pretty much the only thing I'd change about it. Why does it have fangs? If it can chew through shells, it shouldn't have fangs; give it a beak. Guess we'll have to change "Psychic Fangs" to "Psychic Crunch" or something. Beak aside, I still really dislike its design. So you know what? Let's make it monochrome and give it actual
dazzle camouflage. Let's make it look a bit more like a submarine too, why not. Maybe its current color scheme could be used for its Shiny form then, or for some laughs we can make its Shiny form yellow for a Beatles reference.
Oh yeah, Wormadam and Mothim exist. Give Wormadam better bulk and make Mothim a better sweeper, I guess.
Tropius is one of my favorite Pokémon, and it's a shame not many people care about it, and that its stats are horrid. Its highest stat is 99 in HP, and it's very slow for a Flying-type. I'd give it better stats all around, especially because you'd think a sauropod would be able to dish out some damage and take it. It gets freakin' Dragon Dance, so it'd be nice if it could actually use it.