If you look at the “offering rates”, you can see the chances of this. This is a “Rare Pack” which happens 0.05% of the time (or 1 in 2000).
The chance of a Rare Pack has stayed the same, but some of the newer packs have alternate types of “Rare Pack”. This set has the “Regular pack +1 card” (that extra card is a shiny) which has a rate of a little over 1 in 20, and this set is the first set to have a “Themed Rare Pack”, which in this case is all of the shiny megas and has a rate of 1 in 20000.
All of this info is in the “offering rates” at the bottom left of the pack screen.
If you look at the “offering rates”, you can see the chances of this. This is a “Rare Pack” which happens 0.05% of the time (or 1 in 2000).
The chance of a Rare Pack has stayed the same, but some of the newer packs have alternate types of “Rare Pack”. This set has the “Regular pack +1 card” (that extra card is a shiny) which has a rate of a little over 1 in 20, and this set is the first set to have a “Themed Rare Pack”, which in this case is all of the shiny megas and has a rate of 1 in 20000.
All of this info is in the “offering rates” at the bottom left of the pack screen.