shiny butterfree's survival was pretty lucky -- butterfree has compoundeyes, which reduces your miss chance, meaning that sleep powder's 75% accuracy is boosted to 87.5%. that's pretty good, but its not THAT certain, and butterfree is pretty fragile and is weak to a lot of types. there were at least 2 or 3 times where my only choice was to send in shiny butterfree and use sleep powder, against something that was definitely going to use rock slide and murder the hell out of me if sleep powder missed.

armaldo is weak to rock, because he's bug/rock, and rock doesn't resist rock, oddly. so rock type attacks were kind of my achilles heel. but on those 2 or 3 times where my only choice was to try for a sleep powder hit with shiny butterfree, it worked every time. thats not that unlikely - 87.5% chance three times is 0.875^3 which is ~0.67, so about a two-thirds chance of surviving all three attempts.

however, there was one time where sleep powder missed -- and i thought everything was over.

BUT ROCK SLIDE ALSO MISSED. rock slide only has 75% accuracy, so again, not thaaat crazy. but pretty crazy!

and of course, the chance of getting a shiny pokemon is only 1 in 8000. ive only found 3 in my life, and ive played a lot of pokemon. beedrill once in my original silver as a kid, flaafy once in heart gold when i was a teen (scared my mom shouting holy fuck in the car), and then this hero as a caterpie. (there may have been others i didnt notice -- some shinies are only subtly different colors, and if you have the sound off and don't see the special twinkle animation, its not that hard to miss one. but anyway...ive never shiny hunted or used any of the techniques they added later to increase shiny chance, and 3 in a lifetime of playing a reasonable amount of pokemon is about what youd expect. but that this caterpie would survive an entire nuzlocke despite being pretty fragile, and despite being used as a last resort those times? pretty crazy!)