I can help! :)
To get the achievement (from where you left off)
-Talk to Robinfur after getting the prophecy
-Go to your nest in the warriors den and go to sleep
(You should now be in a colorless area(nightmare)
-There is a mysterious cat you will have to talk to 3 times (in fireclan)
-1st time is the leaders den
-2nd time is at the beach by medicine cats den
-3rd time is by the clan meeting area(area next to leaders den with a tree)
(You should now be awake)
-go talk to Robinfur