*None of the starters have any abilities, except for Blaziken which has Flash Fire. This confirms two things, one that Torrent/Blaze/Overgrowth were late game additions and that Blaziken got the most love out of all the starters thru out the development
*Poochyena has no ability, while Mightyena has Sturdy. Similarly, Zigzagoon has no ability, while Linoone has Intimidate. In the final game, Mightyena gets Intimidate and neither get Sturdy. Not sure what the train of logic here is, but it's interesting to see that first and even second stage evolutions might not have had abilities at one point.
*Wurmple has nothing, Silcoon has Swift Swim, Cascoon has Chlorophyll and Beautifly has...Volt Absorb. Dustox eats shit as it has no ability. Okay, I guess abilities were either shuffled about or not thought thru yet. Still, if Beautifly had both it's original high stats and Volt Absorb, it could have been quite a good Pokemon. To add insult to injury, Dustox is still Bug/Flying here instead of Bug/Poison.
*Seedot and Shiftry has no abilities, Nuzleaf has Immunity. Interesting choice, but Chlorophyll and Early Bird are just much better.
*Taillow has Immunity while Swellow has Insomnia. No clue what the logic here is, but this resistance to status must have inspired the later change to giving both Guts
*Shroomish gets nothing, but Breloom gets Speed Boost. Now this is interesting, imagine how retarded it would be to have a Spore mon that has Speed Boost, especially in Gen 3. Absolutely broken, now I want to see this in action. Maybe that's why Swellow has Insomnia? Cut lore on how it developed resistance against it while hunting Brelooms, perhaps?
*Spinda has Oblivious and Cloud Nine(?) instead of Own Tempo. Spinda was never going to take the world of competitive Pokemon by storm, but letting it keep Own Tempo is probably for the best.
*Wingull gets Compoundeye, while Pelliper eats shit. I guess we know why in the final game it has Keen Eye, still the line is absolutely useless until Gen 7 anyways.
*Surskit has Water Absorb while Masquerain keeps Intimidate from the final game. Not sure how useful Water Absorb was going to be on a first stage Pokemon, honestly I just want that stat boost to Masquerain back.
*Wailmer has nothing while Wailord only has Water Veil, only one of it's two abilities in the final game. Clearly unfinished or not thought thru properly.
*Both Skitty and Delcatty have Run Away on top of Cute Charm. I guess it makes sense, but for the sake of the dozen people who raise this thing competitively(me being one of them), I am glad we only got Cute Charm.
*Baltoy line has Soundproof over Levitate. Oversight more than anything else, considering how even it's early dex entries talk about it levitating.
*Torkoal has Flame Body instead of White Smoke. Not really a game changer, again I just want higher stats back.
*Sableye would have had Insomnia on top of Keen Eye. Now this would have made it extremely dangerous, as much as I would love to play with it I would absolutely hate going against it. In the end, it's for the best Sableye was nerfed.
*Barboach line has nothing yet.
*Luvdisc has Cute Charm instead of Swift Swim. So in other words, they took away the only decent thing it has, Speed, and nerf it for a lore ability. Luvdisc can just never catch a break!
*Corphish line had no Shell Armor yet. Pure Water at this point.
*Feebas would have kept Marvel Scale just like Milotic.
*On the inverse, Carvanha has Rough Skin while Sharpedo has nothing.
*Trapinch would have had Sand Stream while Vibrava and Flygon would have had Compoundeyes. Not gonna lie, Sand Stream Trapinch would have been all sorts of interesting: Trapinch actually has just as much Attack as Flygon, just with pathetic Speed and Defenses. Moreover, only Tyranitar has Sand Stream in ADV if I recall correctly, giving Trapinch a genuine niche outside Little Cup. Remember, it can actually fight back if it can outspeed the opponent or take a hit, which is not impossible. Vibrava and Flygon would be useless tho, as they would not be immune to Ground anymore. Vibrava is especially useless as it is just pure Ground type at this point.
*Makuhita line would have had Pure Power. Now this is interesting, in my last post I noted how this looked to originally be a Pokemon that depended on brute strength alone, just like Machop line. Well, it looks like I was right, and a change was made later on to make it more of a technical Fighting type. I don't need to point out how broken an already high Attack Fighting Type with Pure Power would have been, we've been robbed!
*Now this is interesting: Elektrike line would have bad Volt Absorb/Magnet Pull, fulfilling the same role of Steel Type removal as Magneton with the added bonus of being immune to Electric attacks like Jolteon. Real shame, could have been a real contender for the Electric meta in ADV right up there with Jolteon and Zapdos as well as an alternative to Magneton.
*Speal gives us an insight into the second ability of his evo line: Water Absorb. This would have been real handy, especially as Thick Fat is also useful. Just like with Elektrike line, this would have given Walrein two very different playstyles, which is a great utilization of the Abilities feature. Cut for unknown reasons, probably balancing.
*Cacnea line has Cloud Nine instead of Sand Veil. Absolutely useless, Sand Veil is the one thing that made it worth using in ADV, before it was banned thanks to Garchomp.
*Speaking of which, Snorunt get Sand Veil while Glalie gets nothing. Placeholder for Snow Warning, predating Abomasnow? Would have made the damn thing much more useful!
*Lunatone gets Synchronize while Solrock gets nothing, confirming that Lunatone came first and Solrock was a late addition. Getting rid of Levitate makes no sense and would have made both much worse.
*Azurill and Wyanut both have no abilities, confirming that baby Pokemon would have lacked them.
*Spoink Line has Early Bird. Useless, Thick Fat Grumpig at least has a niche, even after it got nerfed. Thanks, Gamefreak!
*Both Plusle and Minun already have Plus/Minus, which means this was going to be the plan from the start. Abilities are still useless, should have completely revamped them or replaced them with something else.
*Mawile has Insomnia over Hyper Cutter and Intimidate. Very interesting choice, but not sure how it would have tailored it's playstyle. At least Intimidate has a hit-and-run advantage.
*Medidite has Water Absorb and Medicham has nothing. Another placeholder.
*Speaking of, Swablu line has nothing.
*Duskull has nothing, meanwhile Dusclops has Pickup on top of Pressure. Absolutely useless and makes no sense, glad it was changed.
*Roselia lacks Poison Point, late addition to the game?
*Vigoroth has Hustle/Guts instead of Vital Spirit. Guts has a lot of potential, Hustle not so much. Wish Vital Spirit and Guts were used alongside each other, would have given you more reasons not to evolve Vigoroth into the big rape ape.
*Tropius has nothing.
*Whismur has nothing, meanwhile Loudred is a Fighting type and has Pure Power. This alongside the debuffs it got makes me think this was originally an unrelated Fighting type that was then merged with Whismur line to make it more useful. Exploud has Drizzle btw, not sure if it makes any sense but it would have been glorious in battle. Imagine a reality where Exploud is OU and makes Rain as retarded OP as it would become 2 generations later, keep in mind that in Gen 3 this ability was unique to Kyogre.
*Clamperl would have had Illuminate and Gorebyss would have had Serene Grace. Clamperl is already useless with Shell Armor, taking that away would have made it even worse. Serene Grace Gorebyss, on the other hand, sounds promising. I would have to look over it's movepool to see if it has anything useful to synergize with Serene Grace, but I think it could potentially be a sleeper hit in the right hands.
*Absol has Trace, probably a leftover from it's Yin-Yang design. This would have made Absol an interesting opponent to fight, maybe make up for it's inability to use it's STABs this generation. Would have been even more useful Gen 4 and onwards.
*Shuppet would have had Insomnia/Run Away and Banette would have had Run Away/Shadow Tag. In the final game, it only has Insomnia, an amazing ability on it's own, but Shadow Tag? Remember, this ability was enough to get Wyanut banished to Ubers, think what it could have done to a Pokemon that can fight back(especially with it's Mega Pokemon stats it originally had). Potential for one of the best Pokemon in the game, reduced to an average one nobody really uses. What a way to go.
*Relicanth lacks Rock Head, potentially a late addition to the game.
*Aron line also lacks Rock Head, seemingly confirming my belief.
*Fossils have no abilities and are pure Rock types.
*Metagross has Pressure for some reason, a useless change
*Bagon line has no abilities, Salamence is pure Dragon
*Regis have Pressure as well, all except Registeel who has nothing
*Kyogre has Static(lol) and Groundon has nothing
*Latis and Chimecho have their final abilities, anyone I didn't mention has nothing.