Probably combo, that's what decides which attack gets picked for others characters. For example Zabuza has 3 attacks, 1 hit atack, 2 hit atack with a more damage, 3 hit atack with most damage and repulse, and with high combo he will do 3 hit more often and 1 hit one less often. So i am guessing it's same for Onoki, with high combo he will fail less and do repulse one more.