Olive had to think fast.
The opponent who got a hold of him was undoubtedly a high-level undead.
Therefore it got two major weaknesses.
Holy magic, and fire magic.
Olive thorough his life has ignored the holy magic - for the most part - since it was customary for the elven elders to be proficient in it, and he wanted to avoid becoming the elder at all cost.
But thanks to that he focused on other types of magic and gained the mastery of fire among other things.
In the situation he was in, using fire magic also seemed like the better option - even if he won't be able to finish off the undead, the forest fire he will undoubtedly alarm the hiding elves far more efficiently than some pillar of light going off into the sky, far away from the village.
As soon as he came to that conclusion, Olive deactivated the thought-acceleration skill and used the strongest of his fire spell while he was sinking into the ground pushed by the cold hand.