Well, for starters, I have to find and catch everything myself, reset games multiple times for starters, etc (Emerald in particular is brutal w/ Johto starters, post-game), and trade them to LeafGreen with a physical cord connecting my GBA SP and my ex's GBA (The "Linking Cord" from Legends: Arceus is actually a drawing of the cord I use). My most recent challenge was finding and catching all Safari Zone-only for dex (Chansey took 3 weeks, it's a pain). Plus, the Legendary Beasts are required for Nat Dex and I have 0/3 (They run and glitch out of existence if you don't Master Ball them), so 3 runthroughs of FireRed are coming up to get them, from start to E4 and side quests to unlock. My LeafGreen (where my boxes are) save file is at about 130 hours, only about 70 of which are playtime (rest is trading time and left-on/AFK time)
