Confidence: It's likely to be this, but I can't be certain.
Notes: Looks liek a willow beauty but your suggestion (in the entry title) that it might be a pug (significantly smaller) is confusing me.
The impression I get here, looking at the Large Yellow Underwing it is with, is that it is the right size for Willow Beauty but that could be a photographic effect.
Can you confirm the size. Thanks.