- Main article: Advanced rulebook#Dominant Player Bug
Player_ID is a hidden identifier in Hearthstone's code that distinguishes the players in a game using ID numbers 1 and 2. Player number 1 may unofficially be called the "dominant player". This has no relationship to which player goes first in the game; in most cases it seems to be determined randomly. It is suspected that this number was not intended to have any effect on gameplay, but a few situations have been identified in which the timing of triggered effects is determined by the Player ID rather than more consistent rules.