Shiny Terrakion Pokémon GO will be available to fight and catch during a special Raid hour featuring the Cavern Pokémon.
Shiny Terrakion Pokémon GO: How to Catch
From 1 p.m. on May 19 to 1 p.m. May 26, Terrakion will be available to battle in five-star raids. There will also be a Raid Hour on May 20 at 6 p.m. for Terrakion.
During the event period, you'll also get an increased chance to encounter a Shiny Terrakion. For Legendary Raids, it seems like there is about a one in 20 chance for encountering a Shiny, so keep fighting until you get it.
Shiny Pokémon won't appear until you get to catch them, even if you battled them in the Raid before. A Shiny Terrakion is brown instead of gray, wth red horns. You'll get a sparkle to denote that the Terrakion you're encountering is Shiny as well.
Terrakion has high CP due to it's massive attack stat, letting it perform extremely well as a Rock and Fighting type attacker. It only suffers due to it's typing, as it has seven weaknesses. It's a glass cannon, but it sure does a good job of being one. Just don't send it against any of the many weaknesses it has.
Those same weaknesses means you can take it down easily in the Raid to get more chances of finding a Shiny. Terrakion is weak to Fighting, Ground, Steel, Water, Grass, Psychic and Fairy.