Essentially, a comp with one DPS only. In the case of Cernunnos, it makes the fight much harder than using a dual core setup (using enkidu/sanzang/scathach to break bar 1 for example), as it requires spreading out buffs across four turns and dealing with the curse on your single DPS.
It definitely helps with the damage rolls but I think she can get by at a lower level. Brave chaining on T2 and using Castoria np on T3 instead might make it easier. This setup isn't perfect either so tweaking it a bit could reduce the RNG needed to pull it off.