In order to be able to access Chrono Castle XI, you will first need a certain amount of MEs. I'm not sure the exact amount, but I was able to access the level after collecting all the MEs from the first 3 worlds.
The premise of level XI is a simple one: use bouncy blue platforms to jump up to higher platforms, and then use that new height to jump even higher on the bouncy platform.
As you go through the level, you will clearly see the coin bubbles and they are very simple to collect. No tricky platforming required.
The achievement will unlock after collecting both coins and finishing the level.
Here is a video for a visual guide: