Blake was torn between his three choices, the myriad of darkness tendrils, the combination spell with Cyra, and also using the second realm darkness bullet spell.
Using the last option was a surefire way for him to end the fight for real with 99.9% certainty, that 0,1% was just a reserved estimation for something that couldn't be predicted by either logic or feelings.
However, 99.9 percent was more than a high enough percentage to ensure his task of killing the intimidating muscular humanoid demon would be completed without fail.
However, there was one important factor that made Blake hesitate greatly to use the second realm darkness spell.