The ice mountain that Bai Long and the others were travelling on was sort of a slow starter. Because with every passing minute the mountain's speed kept on increasing until it finally reached a speed which even Bai Long couldn't fly at.
Upon further confirmation from Qingling, Bai Long found out that there was even a special array which allowed to boost the flying mountain's speed.
But using it consumed the Qi accumulated over the years inside the mountain too fast.
And using it would force them to stop the mountain part way and wait almost half a year before the mountain stored enough Qi for them to reach the Mainland.
That too if they travelled the rest of the distance at its normal speed and not by using the boost.
Still, it was quite awesome that the flying mountain had a function which allowed to increase the speed if the situation called for it.
