Ok so after some search apparently every pokemon that is part of the undiscovery egg group will have guaranteed 31 IVs in 3 stats.
This egg group includes all the legendary, mythical, ultra beast, paradox pokemon (minus manaphy). Includes the baby pokemon, unown, nidorina and nidoqueen (not nidoran female).
Also for the shadow pokemon i dont know if it was changed but across my 2 saves, every shadow pokemon that i have, have 20 IVs in all stats. Maybe the 10 IVs was in earlier versions?
I dont think i have any prism pokemon so i will just believe the information :)