Vader mumbles 'you under estimate my power' over and over again in deep bass like tones that emit from his mechanical voice box, wordless sounds. The stumps of his mechanical appendages drag along the ground stirring up a cloud of black sand from the scorched earth. Vader draws in a raspy breath, the inorganic wheeze of his iron lung, pathetic. This is the place of his re-birth, where he became less than and more than a man, a servant of the dark side slaved to this being, Sidious.
The troopers take a few hesitant steps backwards from the flesh and metal, the power play before them is uncomfortable, dangerous. The Emperor passes beyond them and looks down at his failure. Disgust, disappointment and amusement, always amusement dance on his disfigured features. 'Well Lord Vader, I hope this little example serves to put matters into ... perspective' and with the last word an ugly smile breaks out across his face.
Vader's hate simmers, bubbling through what is left of his organic body but it does not control him like it once did. Sidious' posturing, the high ground and this place no longer holds that power over him. For Luke, his son, has shown him that there are other paths, less direct, to victory and to power.