Dozens of replicas had to die before Lucifer finally understood Ryan's tricks… at the very moment of the activation of the skills he used, he used Energy Control to convert stamina into mana. Using the rest of his stamina, he increased the Power oF Concentrated Strike and killed hundreds of demons.
"Against opponents of this level, he can fight them without a bow," Lucifer thought. "I didn't think Chronus' power would increase his power so much."
When the replicas tried to steal Ryan's stamina and mana, Ryan used his health to convert into energy in the activation of his attacks, and when Lucifer tried to steal that was well, again, he didn't have enough replicas to prevent Ryan from attacking. Just absorbing the replicas would give the chance to overpower Ryan though and through, but that wouldn't satisfy Lucifer. He knew that Ryan wasn't someone who would give in to despair that easily. After all, he came to challenge him alone.