Pokemon gets a lot of flak for churning out the same game over and over again, but a lot of changes have been going on under the hood with each new generation. Don't get me wrong, I'd love to see Pokemon be a bit more ambitious and playful with the formula - which is part of the reason Scarlet & Violet is my most anticipated mainline title in years - but there have been notable changes throughout Pokemon's lifetime. Terastallising, the latest gimmick to arrive in Scarlet & Violet, might be the most effective change yet.
I often think of Pokemon as I do the sports sims like FIFA, which I also pick up every year. FIFA gets criticised for being the same game every year, but if you pick up FIFA 17 now, you'll notice major differences to how the game plays. Likewise, Pokemon has stuck to hitting eight gyms in a set order, then the Elite Four, accompanied by familiar obstacles like a villain's lair, a cave, and a forest, but battling feels very different in each game - even if we perhaps don't always notice it.
Pokemon has changed itself in similar ways. HMs used to be needed to get around, meaning your party would either have a HM Slave like Bibarel, or you'd have one of your 'mons waste a move slot on Cut. Now they've been eliminated, only useful moves like Surf or Fly remain in use. We've also had the Physical/Special split, which revolutionised how Pokemon work in battle. It effectively doubled the amount of stats you have to consider at a competitive level, and reshaped each move individually. It's not a thing casual players tend to notice, but adding Special Attack and Special Defense to the stats alongside Attack and Defense might just be the biggest change to the formula Pokemon has ever made. At least, until Terastallising came along.
Terastallising is another 'one per battle' gimmick, much like Megas, Z-Moves, and Dynamaxes before it. Of those three, only Megas had any notable impact, and the biggest thing Megas have influenced in Pokemon's canon is starting off a chain of copycats. Dynamaxing and Megas have some minor differences, but they're the same idea cooked in two different styles. Terastallising is not just a new version of Megas or some fancy visual flair that temporarily makes your Pokemon more powerful, it involves changing a Pokemon's type - something which has never happened before.
Type is the single biggest factor in Pokemon. The wrong type can mean attacks against you can do up to four times as much damage, while your own attacks can be limited to just 25 percent effectiveness, or even do no damage at all. Pokemon have a set type and it cannot be changed, ever. Evolution may change a Pokemon's typing, but that cannot happen mid-battle. Even if the first round gives your 'mon enough XP to level up and evolve, the evolution itself will not happen until the whole battle is over, meaning you could be ready to level up and still have to defeat up to five more 'mons before you can actually do it.
Terastallising changes all that. Switching types mid-battle adds an extra layer of thought to proceedings, especially as it can only be done once. With Dynamax, the obvious answer there is either your most powerful Pokemon or the one who already has a type advantage and wants to double down. Terastallising offers more of a risk, but potentially more of a reward. We'll need to try it out before we can see exactly what impact it will have, but it could be Pokemon's biggest evolution yet.