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Consider Leratiomyces ceres and Stropharia rugosoannulata.
Possibly young Armillaria.
Could also be Cystoagaricus trisulphuratus
This looks really quite small and in the incorrect habitat for A. muscaria. Is that moss on wood? Consider Leratiomyces ceres.
I don't think it's a typical shelf-fungus (Polypore). I think I can see a tiny bit of stem poking out towards the tree and maybe some faint gill like ridges around the margin. I'd guess Pholiota.