Jay used the second skill 'Gravity Control'. Of course, it cost him no MP to cast that.
Well, that meant that the skill wouldn't have been powerful at all. That's because if it didn't rely on the host's MP, then it might have relied on the MP inside the globe or the surrounding which wouldn't have been much.
That way, the effect of the skill would be weak, at least, that's what Jay thought.
He thought that the skill wouldn't do any better since he had seen its power earlier. Although it was able to pin down the enemies earlier, it was only because they were weak.
In front of someone who is strong, tricks won't work easily. And weak skills wouldn't have much effect at all.
Over 80% Of the spider's MP was left white was quite a lot.
Jay had no way other than using someone's other skill at the same time to aid the Gravity control and stop the spider from moving.