Bit late, but the boss Revavroom look to be entirely custom mons that are generated on top of the previous mons in the battle.
For example, vs. Giacomo, you fight a level 21 Pawniard with 25 IVs across the board and Hardy nature.
Afterwards, you come up against a level 20 "Revavroom" with 0 IVs and EVs across the board, Serious Nature.
Its stats are: 160 HP / 36 Attack / 47 Defense / 35 Special Attack / 38 Special Defense / 129 Speed
These are pretty interesting for a level 20 Revavroom.
View attachment 481766
What's extra fun is that the Species on the battle data is still Pawniard, which suggests to me that they simply edited the values into a custom car when transitioning into the battle. (And maybe why you're not given a chance to switch Pokémon?)
Whatever they did to create the custom Revavroom isn't the same as creating regular mons, which explains why they're not in any trainer team dumps and why people can't hack them in -- you'd be creating something entirely custom if you want to copy it.
Here are all the stats (actual stats, not base stats) for the different Revavroom. They obviously don't make sense with the IVs/EVs/Nature.
Code:
Dark: Level 20, Intimidate, Serious Nature, all 0 IVs/EVs, 160 / 36 / 47 / 35 / 38 / 129
Fire: Level 26, Speed Boost, Serious Nature, all 0 IVs/EVs, 204 / 49 / 60 / 29 / 51 / 128
Pois: Level 32, Toxic Debris, Serious Nature, all 0 IVs/EVs, 252 / 60 / 80 / 50 / 70 / 130
Fair: Level 50, Misty Surge, Serious Nature, all 0 IVs/EVs, 380 / 90 / 120 / 70 / 90 / 132
Figh: Level 56, Stamina, Serious Nature, all 0 IVs/EVs, 408 / 95 / 120 / 80 / 85 / 131