For a short while for the Wild Area event #14, players were able to encounter a Drilbur with Hydro Pump, exclusive to Shield 1 star raids.
While it was possible to obtain this legitimately, Game Freak is treating it as though it didn't happen, and this Drillbur cannot be used online.
Back when the event was still ongoing, the Wild Area News was updated, and Drillbur can no longer be encountered with Hydro Pump, effectively fixing the error.
Any players that did not update their wild area news, or have already caught one, will have the Drillbur unchanged.
It is not known if this Drillbur can go into HOME (at time of writing).
For the time being, this Drillbur will be classed as illegal.