It's okay Zeron, Ragna is more advanced than he looks, specially compared to Hazama who has fewer combos.
Honestly? Don't care much about that challenge, there are better, easier, optimized and pratical versions. Here, this is one might be easier for you since it doesn't require Hell's Fang loop:
FC 2C 214D 2C 5C 6C (DC) 6B BK 22C (RC) ,dash 6D whiff j.D, 5D(1) 214D 6D (JC) j.214C dash 5D (1) delay 623D~Heel Drop falling j.D j.214B~214D 5D 214D (dash) 5D DbD
Damage:8923
Notes: D ID must twice. Strict BK timer.
However, if you're doing it for the sake of completion, well... train the loop alot, it's a matter of feeling.
You can get better mileage off that, like 5K+
2 Deadspikes in the same combo are a no no, except for BK.