Veer had a few goals on his trip to this unknown forest. First, he wanted to get used to fighting in the dark. Second was related to the first as he just wanted to battle someone to check his limits.
Then, he also wanted to search the whole forest for any clues. He guessed that the barrier Rain mentioned was a Rune Formation, so there must be a core for it.
He only managed to crack the Wheat Farm Rune Formation because he found the core, or at least that was what he thought. He still had those fifty Dark Metal Slates, which could come in handy later on.
So, he was hoping to find something similar here so he could escape the forest without fighting the snake. The last objective of his trip was that snake, whom he wanted to observe and find its weakness.
Fighting the unknown was stupidity.