Bael is encountered as the level boss of Mission 4 at the first half-section of the game then the rest will be Dagon instead in Mission 15 and Mission 19.
Mission 4 - Quick Rusalkas
This is the fastest method but, if your EX-Streak does not whiff then Buster won't work
Snatch → Buster is more consistent which requires third hit of RQ before CS'3
Mission 4 - Bael Phase
CS'3 detonation has different timing between Breath and Jump Press. Make sure that the explosion will hit Bael during the knock down state
Frog can easily kill your run if it stays passive and doesn't provide you two main patterns for setups which are Breath and Jump Press.
Mission 19 - Dagon
JC the 3rd hit, then Helm Breaker → Stinger JC the 3rd hit, Divekick, Coyote-A shot JC the 3rd hit, Helm Breaker, Straight
Nero [M4 Bael] - Jump Press cycle example
Dante [M15 Dagon] - Standard cycle
Nero [M19 Dagon] - Eat cycle example
Nero [M19 Dagon] - Jump/Breath stun example