To unlock "Ada's Demise" you must complete the fourth chapter of Ada's campaign on any difficulty.
There are many cross-level medals available, and the unmissable story medals but only two chapter specific medals :
*Killed off your imperfect doppelganger
*Cleared the chapter without being spotted by the enemy
In this chapter, you can also earn :
There are, as usual, serpent emblems to collect. See the video for the emblems. Video credit goes to the creator.
*Any questions, or corrections with regards to medals, please let me know and I'll adjust.