Units with Arena Type 9 have the following AI:
- 10% chance to BB on the first turn
- 50% chance to BB
- 20% chance to BB when HP is under 50%
- 40% chance to BB when 1 party member is present
- 30% chance to normal attack enemy with lowest HP remaining
- 100% chance to normal attack random enemy
In short, there is a 55% chance (64% chance if user is under 50% HP) of the unit with Arena Type 9 to use Brave Burst skill. Assuming the best conditions, there is a 78.4% chance to use Brave Burst skill.