Hello ! So the percentage of chance to apply the buff grows linearly with the number of priests . That said , with n priests , you get 0 . 05 n chances to apply the buff every 10 levels . The chance of non applying the buff follow this law Pno spell 10 . 05 n # lvls 10 P applying spell 1 10 . 05 n # lvls 10 Then you get approximately this Chance of applying buff with 4 priests after 10 lvls 20 % 20 lvls 36 % 30 lvls 49 % 40 lvls 59 % 50 lvls 68 % 60 lvls 74 % 70 lvls 79 % 80 lvls 83 % 90 lvls 87 % 100 lvls 89 % You can do the same with 3 and 5 priests using the same formula . But if you want to optimize the time needed to climb to a certain stage , it becomes a bit more complicated . I might write a script for it if several people are interested .