>>35467784Gyarados, Lake of Rage like almost everyone playing early on. Full odds. Literally, lol.
But if you mean something not given to you... Paras in Mount Moon in Gold was the first one. Though that was my fourth encounter with one.
First three I encountered were actually...
>Bellsprout on Route 32 right next to Violet City (was training for a couple minutes before the Gym since Mud-Slap can really fuck you over with Cyndaquil), crit killed it.>Koffing, stupidly forgot to buy some more balls after catching Sudowoodo and Stantler before reaching Ecruteak and entering the Burned Tower.>Weedle, bug catching contest, was multi-tasking and didn't comprehend the Shiny sound had gone off while looking for Scyther before auto-hitting Run.>>35467833It really depends upon how long you play and what games. And what you're willing to do. It's pretty damn easy to RNG abuse in Gen 5 in particular. At least the first ones.
In B2/W2, they're so incompetent they fucked up the egg code so it's almost impossible to RNG breeds on B2/W2. How they managed that fuckery one will never know since literally nothing changed about breeding in between (not even new egg moves like usually happened in follow ups up to that point) meaning it should've been a copy-paste. But anyway...I found a bunch early on as I've just mentioned but then there was a long break.
After Paras besides ones I was traded I didn't see another legit Shiny until about 8000 hours into Emerald (friggin' SZ Pikachu that ran). Didn't even get a Shiny in the Odd Egg in Crystal though my brother did.
But now I've got hundreds. Some are RNG abused and events but most are between full odds and Masuda. Hell, a third of my battle ready Gen 7 mons are Shiny and I've only got about 1,900 hours total in this sad ass Gen.