User blog comment:Dragonzzilla/Custom Content/@comment-5618636-20140215210142/@comment-1888392-20140215224727

Unlike, who can cast from a distance perpendicular to herself, Fenris' ice trail follows him. As he leaps through the air, the ice wall forms behind him as far as he jumps. It's much more risky for this reason, in addition to having a shorter range than.

In order to properly use White Walker, Fenris must outrun his target, or alternatively flank. If he's chasing somebody and leaps, the ice wall will still be behind him; he needs to get in front of his target, or at least neck-to-neck, to box in his target. But if he keeps leaping (of which, there is small margin for error), he's going to starve himself of mana and be vulnerable to counterattack.