Toucannon asks:

So, MegaEvolution is something of a base-breaking point for pokemon fans, but you’ve been known to mention it being a good thing for some pokemon (in terms of improved useability). Thus, I ask: which of the 50 or so existing megaevolutions would you say are necessary and worth keeping, and which ones are superfluous and shouldn’t have been introduced at all?

Well… based on that particular criterion, probably fewer than half of them were a good idea, maybe even fewer than a third, which is a pretty terrible success rate.  Terrible enough, in fact, that I think it’s pretty clear this rationale wasn’t really a major part of Game Freak’s process for deciding which Pokémon to give Mega Evolutions to (even though it’s something I like), and therefore arguably not a good way of judging them.  Particularly in the first round in X and Y, Mega Evolutions primarily went to Pokémon that were already fan favourites, like the Kanto starters, Mewtwo and Gyarados, and most of those were already at least decent.  But… well, you asked, so okay, let’s make a list…

Venusaur, Charizard, Blastoise, Aerodactyl, Houndoom, Gardevoir, Medicham, Abomasnow, Slowbro, Sceptile, Sharpedo, Gallade: these were arguably fine. These Pokémon have had mixed fortunes over the generations, and the ones who were around for them had mixed reactions to the mechanics changes of generations II and IV, but as of generation V, they were doing quite well.

Alakazam, Gengar, Gyarados, Scizor, Heracross, Tyranitar, Garchomp, Lucario, Swampert, Salamence, Metagross: these were definitely fine; I don’t think any of these Pokémon have ever really been bad at any time in the games’ history, except arguably Gyarados in generation II (after splitting the special stat, but before the introduction of Dragon Dance), and some of them have always been amazing.

Mewtwo, Blaziken, Latias, Latios, Kyogre, Groudon (those last two are technically not Mega Evolution, but it’s basically the same thing): clearly didn’t need help; these were all pretty solidly in the “too strong” bucket already – Blaziken thanks to Speed Boost, Latias and Latios partly thanks to the Soul Dew, Mewtwo thanks to SCIENCE, and Kyogre and Groudon thanks to being basically ancient gods.

Kangaskhan, Absol, Banette, Steelix, Altaria, Lopunny: well, they weren’t fine; I can certainly accept these as being in need of some sort of extra kick, but there were other Pokémon who were worse off, and Mega Evolution seems fairly drastic as a rebalancing tool in these cases.

Diancie: Bit of a special case, since Diancie didn’t exist prior to the introduction of Mega Evolution and there’s no point of comparison. There’s sort of no verdict I can give on Diancie that makes sense in this context, but I think if it had access to Magic Bounce without Mega Evolution it would probably be fine, though not amazing.

Rayquaza: what the christing hell were they thinking

So the ones that were, in my opinion, clearly a good move from the specific perspective of using Mega Evolution to buff a weak Pokémon were… Pinsir, Ampharos, Mawile, Aggron, Manectric, Beedrill, Pidgeot, Sableye, Camerupt, Glalie and Audino.  Six more in the Kangaskhan et al. bracket makes… 17 out of 49 (not counting Diancie).  There are perhaps others that I don’t strenuously disagree with, but my rationale would still have been very different.  I would’ve been tossing Mega Evolutions out to Pokémon who’ve never had a moment in the sun, like Torkoal, Alomomola, Sunflora, Castform, Stantler, Mr. Mime, Kecleon, Mightyena, Farfetch’d, Dewgong… for goodness’ sake, Delibird.  But at the same time, there is an argument that doing things my way would have not had the same appeal to the fan community or fully embraced the things that most players actually seem to like about Mega Evolution.  People like it when their favourite Pokémon, who is already awesome, gets to do something even more awesome, and Charizard is more people’s favourite Pokémon than Stantler (…and… well, rightly so, frankly).