While catching a Mythical Pokemon can be challenging, getting a Mythical Shiny is more complex. Shiny Genesect is a collector's item due to its all-red look. The easiest way to get a Shiny Genesect (Burn) is to win the Genesect (Burn) raid.
After defeating the legendary Pokemon GO raid boss, Shiny Genesect (Burn) may appear nearby. While there's a chance of some trainers encountering a shiny, some might not since a shiny encounter isn't guaranteed. Trainers must participate and win multiple raids to catch up to its Shiny spawn rate and encounter a Shiny Genesect (Burn).