The chance of finding a shiny has dropped to 1/4096, and in a horde battle you meet 5 pokemon at the same time, so the chance is 5/4096 in a horde, which also means 1 / 819,2
The chance of finding two is 1 / 838 860,8
The chance of finding three is 1 / 1 144 457 789,44
The chance of finding...