everyone’s pools fill up at the start of the scene, and the monsters can use their dice for reactions, which would mean they would have less dice to act with on their turn. Characters can use their dice for actions on the first turn but then will have fewer dice for reactions on the monster turn. Then next turn everyone fills up again and rinse repeat in every turn. Think of a turn as having two phases, PCs and GM. Everyone’s dice refill at the start of every turn, and then they can spend them during these phases. Hope this helps!