For the Evolution achievement, you need to talk to Lukka after reaching the meteor and touching it, you will have the option to tell him about the event (not sure if you need to have helped him with his demonic essence experiment prior to unlock this conversation). Afterwards he'll ask you to wait a couple of days to let him figure things out. Soon you'll have a new conversation topic from him, in which you can give him essence to conduct a new experiment. Good luck!
The Warden is a demonic entity who roams the Eastern Barrens. He's pretty easy to find, not much to this one.