Unmodified highest Speed stat will gain Priority (i.e., excluding buff/debuffs) during battles. Some Creature abilities also allow the opponent to gain Priority despite having the lower Speed stat. 
 
Speed Ties are resolved as follows: 
  • If Creatures have the same Speed, the Creature with the higher Level gains Priority.
  • If Creatures have the same Speed and Level, the higher Rarity gains Priority.
  • If Creatures have the same Speed, Level and Rarity, the player that chooses an Ability first will gain Priority.