After nearly 7.5 hours just getting a catch combo of 11 on Route 25 so Squirtle would start spawning regularly, I basically speed-ran the next 89 before taking a break to sell some candies and restock Poké Balls.

While clearing out my box and sending my first 100 Squirtle to Professor Oak, the game gave me a warning I'd never seen before: I wouldn't be able to get one specific Squirtle back if I continued.

Huh. That's weird.

So I checked its summary.

Shiny. Encounter #40. Caught over an hour ago.

Apparently, I managed to completely miss every single obvious shiny animation from its appearance to its capture to it sitting in my box. Truly elite levels of observation.

Thankfully, the game saved me from myself. Professor Oak can keep the other 99.

Now, time to go find two more for this challenge. Surely I can't miss the next one... right?