Tainted membrum had always been unlockable, the main issue players have is usually finding the tentacles Regen. They are dropped from the Void Octopus at the storage area of the Voids castle Kitchen. You can check your bestiary which will show you the drop chances of items for each monster. In the current version of the game, there's a glitch making The Voids Shadow and other turn counter based enemies imposible to kill. This will be addressed in this week's update. I knew about the issue beforehand but I was forced to drop the Itchio update early since I was unsure if the game would disappear out of no where. Other than that, you can check the discord for info on updates, report bugs etc.