Once he powered the sword with as much mana as possible, Bardeelus simply waited for this angry beast to arrive. He had to test this sword out on something, and this was a great opportunity to do so.
Once he sensed that the beast was less than thirty meters away, he simply swung. This thing approached fast, and he just knew that it would get here in front of their feet, in a matter of seconds!
After he swung, the sword just slipped out of his hands, and then flew towards the target. Now regarding what happened next, they couldn't see the details all that much because everything happened in less than a second. However, they did see the results!
An explosion erupted, but it wasn't the kind that would destroy everything in its close proximity, it didn't even have a resulting shock-wave, no. The blow only exploded the sole target into a million pieces, and the aftermath was only a cloud of mana, rather than a crater of any size.