The Mysterious New Skill was a phenomenon whereby Jagex officials remind their players
OVER 9000 times per second as frequently as possible that a new skill is coming out. When pressed for details, they suddenly disappear, whilst repeating the word soon.
The Strange Power that molested players in January was actually a teaser, but all the players were predicting an epic boss fight and this slipped them by. Even when a big-ass castle occurred one day, it didn't click in their minds at all.
It later turned out to be the
minigame new skill Dungeoneering. Which was a bit anticlimatic to be honest. Look, just click here and GET OUT OF OUR SIGHT.
There are more occurences of Jagex mentioning the new skill than there is use to it.