Here is the full list of all 10 Ramayana achievements.
Finished Tutorial. i.e. Finished First 2 Chapters under Campaign Menu
Set fire on water
Use Hanuman's Giant form against Kumbhakarna
Create a custom map
Kill kumbhakarna and complete Chapter 10
Kill Meghnaad and complete Chapter 12
Use Brahmastra
Kill Raavana and complete Campaign
Complete chapter 17 to lift Gandhamadan Mountain
Construct Rama-Setu and finish chapter 5