There are 3 main ways this could have happened.
Glitches: The main Glitch that affects shiny rates in the Cute Charm glitch. This page over here explains the glitch, but yeah, if you had a Pokemon with cute charm as your lead, this is probably why you encountered 3 shiny Gligar. Also this, RNG manipulation.
![](https://www.smogon.com/ingame/rng/dpphgss_rng_intro)
Luck: The 3 Shiny Gligar could also just be plain luck, although there is a very slim chance this actually happened.
You have a fake copy/reproduction: If you have a reproduction, there is a chance the person who made the reproduction, accidentally tinkered with some of the code, causing some of these rare occurences.
I hope this helps
![](https://pokemondb.net/pokebase/215161/i-need-help-with-the-cute-charm-glitch)