The battle against PULSEgrowth in Obsidia Park is memorable to me as a marker for the exact moment I fell in love with the game. Though less for the battle alone and more for the entire scene. Hah~
I was skeptical about whether or not I'd like Reborn at first, and while my impression of the game wasn't bad at all up until Obsidia, it wasn't until I got to fight my way through the overgrown park that I really got sucked into the game's atmosphere.
I miss the old forest map for this reason. While I know why it was removed, I immensely enjoyed how tense it felt to navigate the place, to see Rini and Amy tangled in the vines, and to eventually be met with the very first PULSE 'mon at the end of the path.
...It was quite tricky, though. I remember Tangrowth having the forest field and electric coverage, which made it a little harder for my dearest Noctowl to take it down. My first attempt had me unprepared, and I was caught completely off-guard when the damn thing shocked my best bird into oblivion.
In the end we did it, though.
Seeing a PULSE 'mon for the first time felt wonderfully eerie to me. The person who got me into the game did warn me that several boss battles had Pokémon with enhanced stats, but I hadn't seen them until then, and was thoroughly surprised.
I am not exactly the biggest fan of Mega Evolution, but the way Reborn used the concept for the PULSE system immediately appealed to me.
I like it when a game allows me to picture what happens in my head, and this fight made it all too easy for me. Imagining my character and Noctowl facing that enormous monstrosity (completely unprepared, never having seen anything like it before), certain that they might be fighting for their lives there, was epic.
The set-up and the fight alone already are enough to make this game moment memorable to me. The fact that it introduced my favourite characters made it even better.
Honorable mention goes to the battle against Solaris at the Fiore Mansion. Man it felt so good to be begrudgingly complimented by the guy.
Something about having the (former) leader of Team Meteor himself acknowledge how powerful you've become is just so satisfying. It's one thing to be respected for your abilities by your allies. It's another thing entirely when it comes from your enemy.