Another holiday side-quest – “The Tower Outta Nowheres” – which is recommended for level 30 players. I’m way past that now (level 45), so can beat whatever the Defensive Regulatory Magicon can throw at me. Even a cow.
The quest “Turn and Face the Strange” is a secondary quest in The Witcher 3 that modifies your mutagen enhancements. You really have to jump through hoops (or rather: portals) to get the prize, though.