Shrinkstools are a powerfully enchanted toadstool, typically found in enchanted forests or other secluded magical locations. Watch your step.
The Slow Death Cap looks, to those who don't know what they are looking at, like an edible mushroom, but eating it is one of the most unwise things anybody could possibly do.
If you want to add a "supernatural" touch to your campaign, define the rules of magic and the universe. Make your players comfortable with those rules. Then your new supernatural creatures must then break those rules.