Eren was inside the fiery realm he had created by himself.
Therefore, the fire-element spells were easiest to cast inside the domain. Their casting time had been already cut short by a lot due to Eren casting them like Hex spells. However, they received a significant boost in their output due to the fire-element mana present all around them.
While approaching the monster, Eren started spamming spells at it. The fire-element chains sprouted from nearly everywhere and bound the blue monster once again. This time, he couldn't get away from them even with his enhanced physique.
"Daryaaav!"
The monster was hurting at this point. His mana defense layer had been breached by flames at multiple points. The breached zones exposed his skin to the flames, which cooked it like it was monster meat barbeque day.
Eren retrieved his axes from his storage and charged them up with his fire-element mana. He gripped them hard before using another spell on them.