Event Only Moves
One of the newer concepts that has been incorporated in Pokemon GO that has been found in the Mainstream Pokemon Games for ages is that of event only moves. These are moves that a Pokemon can't normally learn under regular circumstances, only knowing such a move because it knew it during a given Promotional Event. In Pokemon GO, Event Only Moves can either be for a Pokemon's Fast Attack or Charged Attack. Furthermore, using a TM to change this move will also not work on these given Pokemon. One example, thus far, of an Event Only Move is Pikachu knowing Surf (only could be found during the first ever Pokemon GO Community Day Event).