“Control Time, control everything!”
The Time Twins, Krux and Acronix are the former Masters of Time. Krux appears as a minor character in Day of the Departed, and the twins act as the main antagonists of The Hands of Time.
During the Serpentine Wars, they assisted the Elemental Masters in their victory, however, Chen and Clouse coerced them into switching sides and tricked them into thinking they had the most powerful element, therefore they deserved to rule the world. The two of them rebelled against the Elemental Alliance, but had their powers stolen and were supposedly lost to time. Unbeknownst to the Elemental Masters, Krux remained in Ninjago, and cultivated a plan for 40 years in the future when his brother would return.
When that day came, they assembled an army of the Great Devourer's spawn and collected the Time Blades to return to that moment in time 40 years prior when they failed. Their plans are stopped by Kai, Nya, and Master Wu, and the two have been lost in time ever since.
They are the former Elemental Masters of Time.