Stillness of Mind really needs to be optional, as it is in "proper" 5E - one option among many for what you can do with your action. Or at least toggle-able. What happens right now is that you automatically use it - burning your action - any time you are Frightened. But losing your action is usually worse than the effects of Frightened, so as currently implemented this ability is a drawback.
Last edited by philosoraptor; 01/10/23 09:11 AM.