Insufficient Mana.

After he had gotten an idea about the amplification his soul power provided to his magic, Ark decided to try out his new skill [Sovereign's Howl]. Since he had no real idea about the power of the skill yet, Ark wanted to use it without amplifying it with his [Chaos Soul]. As he had a bunch of other magic he also wanted to try out, he decided to use up about 10% of his total mana to try out how effective the skill really was. 

He felt like he needed to spend at least that much to get a good idea about the destructive power of the skill, without going overboard. Since it was a skill that could be combined with other skills, Ark decided to combine it with ice magic since he felt like he had a pretty good idea of the power of his ice magic. 

"I'm going to use a rather large move next, so you should probably take a few steps back."