To defeat a Demon of such great power, especially this one who could predict the next future movement and easily avert it, Snow had to think of a way to bring him down.
Now, Zarmon's real powers weren't really known. Not just that, but the fact that this form he uses only gives out about 50% of his powers. If he could show his true form and open the gates to Didon, the whole village would be wiped out, no doubt about that.
Having noticed Zarmon couldn't actually predict 'super-sonic' movements, but also can't follow spells which are wrapped around the attack, Snow had to go all-out on him if necessary. And even at that, could he be able to defeat one out of the two, Highest Ranking Devils of the High Table?.
"Your thoughts are deep. Curse you Vin for helping him" Zarmon broke the silence. "I wonder what you're doing now? If you dare protect those disgusting humans, then it will be the end for you!."