Our neighbours showed us this, in late October growing just across the boundary in a grassy path in their wood. We’re pretty sure it’s a Verdigris Agaric (Stropharia aeruginosa). Not in our wood yet though (sad face). May be next year. Naturespot tells us to look out for it on grass in woodland areas between July and October. It says the cap is bell shaped when young but flattens later. The stalk (stipe) is quite long and of uniform thickness. It has a fragile brown/black ring, and below this the stalk is covered in fine white scales, or flakes. Not that there are many green mushrooms to confuse it with.