Salamence. That thing nearly drove me insane. Eventually I had actually caught it. But I forgot to save, took on Charizard (also a total struggle) and failed. When I realize I hadn't saved, it was hard for me to suppress my pure rage and anger at myself for not saving. It also was hard because it was the middle of the night.
In Ranger 2, I have to say Drapion. That thing held a barricade on my progress in Almia. It was so infuriating! In fact, it might just be the reason my DS has a really floppy top screen.
In Ranger 3, I haven't seen Arceus in the past yet (but I still have the event in the present) because I'm stuck at that Weavile in the Ice Temple. So hard with infuriating speed, even when I have a Blaziken partner.
3DS FC: 4597 - 0384 - 5442
If you add me, PM me with your friend code and I'll add you.
Friend Safari: Grass; has Oddish, Ivysaur and Quilladin