Most of the hidden achievements in KoA seem to resolve themselves through normal game play (defeat this guy, complete on hard, etc) so I imagine the answer to this one is going to be along the same lines.
- Give Her a Hand
- Keep on Rising
- Manic Pixie Dream Elf
- Message in a Bottle
What are the requirements of these 5 achievements? (I should note that Steam shows 0.1% of players have achieved them, so they are being awarded.)