>>14833330Shiny chains require pokeradar, which in BDSP you only get after filling regional pokedex.
>>14836154Once you have pokeradar(see above), recatching the same pokemon in the same area in one play session raises the odds every time you do. Starts at 1/8192(normal shiny rate) and goes up to 1/200 after 40 consecutive catches. Failing to catch or catching a different one resets the chain.