As someone who’s played (almost) every main series game at least once and has actually completed the main story of every generation since 3 at least once, it’s very hard to impress me with an NPC Pokémon battle, in large part because the games are so easy on account of being made for players of all ages- which for all intents and purposes means these are kids games. Kids games are fun to go back to for nostalgia purposes from time to time, but rarely do these more accessible games have the same level of complexity that’s easier to appreciate as, in my case, a young adult.
I mention all of this because, for me, the difference between a good Pokémon battle and a great Pokémon battle is all within the buildup to the fight. The story writing, the implications left by the characters, how difficult it actually is to reach the battle in question; these are all factors that can make a fight more memorable if handled correctly. Well designed battles have a tendency to also be some of the most enjoyable and/or fun, and if I had to pick one battle from the core series games that does this the best… I’m going to be honest, I’m not sure I could. Simply because none of them have impressed me enough. That isn’t to say that some battles aren’t harder than others, of course. Gym Leaders that specialize in tricky Types to deal with in their respective games for their point in the game come to mind, but even then most main story battles throughout the entire core series don’t make use of stuff like EVs and competitive movesets. The one time that comes to mind when they did do this is unfortunately attached to the rest of BDSP being stupidly easy up to that point, though I suppose it beats Platinum’s Elite Four having no competitive movesets and lower levels at the same time.
But what about the spin-offs? In a sadly far too common case of “slept on spin-off titles do things better than the main series” (this isn’t just a Pokémon problem), there’s quite a few major battles I can think of that have left an impression on me. On the “standard RPG style” side of things, we have Evice from Pokémon Colloseum, a fight that gets a lot of slack because of the brutal difficulty curve but when me and a close friend tried to beat him for the first time not too long ago, I found that navigating this fight felt less like an unfair difficulty spike and more like a fun puzzle to complete. What strategies with Colloseum’s limited options were the best fit? What ways could we use to try and bridge that level gap with as little extra grinding as possible? By comparison, this isn’t like, say, the postgame of Black & White 1 where your team is in the low 50s and all these Trainers have stacked teams in the 60s or higher, or the battle with Red in the Johto games where the difficulty jump is arguably a bit too large, especially in Gen 2 with limited grinding options for that late in the game.
On the “action spin-off” side of things is where things get really interesting, though. The boss fights of the Pokémon Ranger games tend to be elevated by the surprisingly memorable characters who are sending these Pokémon out for you to calm down, and some of these across the trilogy can actually be deceptively challenging to go along with it. I would hardly consider these action games as much as something like Ranger, but some boss fights in the Pokémon Rumble games also come to mind, more specifically the Cobalion battles in the 2011 3DS installment Rumble Blast. You actually fight this Cobalion twice in the game, and the first fight is a very rare instance of a forced loss battle in an officially licensed Pokémon title, which combined with the unironic surprisingly deep lore of a game about chibi toy Pokémon creates a much welcomed desire for the player to continue playing and eventually come out on top later in the game’s main story.