Doppler mutagen is an alchemy ingredient in The Witcher 3: Wild Hunt and is used to craft Doppler decoctions. They act like lesser red mutagens when placed in the diamond-shaped slots in the character panel.
- The player only has one chance to receive this mutagen: during the quest An Elusive Thief. However, if the player leans towards being merciful, they can miss this chance and must either forego making the decoction, use one playthrough to kill the doppler, or use console commands to get the mutagen.
- While a doppler can be killed during Contract: Skellige's Most Wanted, it doesn't appear to drop a mutagen.
- In an undocumented change for Patch 1.08, all mutagen icons were changed. However, there was still a bug for those on Steam and Origin that didn't reflect this and was later fixed in Patch 1.22. Despite this, some may still see the original icons instead, even with a fully patched game.