With GameMode X new achievements are available. They have a pop up and will show the "Achivement Get" text in the chat, but won't be displayed anywhere else. This is just a visual and announcement feature then anything else.

List of Achievements

Achievement How to get it
Improved Crafting Craft an Advanced Crafting Table in a normal crafting table
Smells like Notch Craft a Notch Apple in a Advanced Crafting Table
Get Risen Die and spawn a Undead Player in your place
An idiotic dead Get killed by the undead version of yourself
Time Flies Fly a total distance of 10 KM (with an elytra)
Take out the Trash Create a Trash Can, by placing in on the ground