“Unfortunately, I made a mistake when I sent you to your destination. I boosted the Endbringers’ power source by accident. But don’t worry, you still have a chance to survive. The powers I gave you are strong enough to resist them for now.”
All the Endbingers have been charged, what this effectively means is that they are no longer holding back, and you can never be sure which Endbringer is going to attack as they no longer hold any specific order in which they attack or how long they stay dormant in between attacks, as well as being around twice as strong as they were before they got the power-up.