Who says it's solid lichen? A werewolf is half man, and half wolf. Therefore, a werelichen, would be half man, half lichen. (Or if you prefer, half man, half fungus, half algae. That's an extra 50% right there, so already this monster sounds pretty deadly)
So, a big guy, thick green skin, thick layer of lichen to pad him against blows. I'm sure it would be at least as dangerous as a werewolf. Make it bigger on account of that extra 50% of being, and it's pretty tough! Can we add extremely fast healing of wounds? Have that represent the symbiotic algae in its blood helping to restitch severed tissues. Sounds like a mean foe to me.
In the 2003 Hulk movie, wasn't he supposed to be green because they threw in some algae DNA? So there you go: Werewolves transform into their "lycan" form during a full moon, werelichens transform to their "lycan" form when they get angry. Scientifically proven fact!
Also, I remember you could kill moss on your deck just be leaving a penny on it, the copper kills it. If lichens are similarly vulnerable, then instead of a silver vulnerability, a werelichen would have a copper vulnerability! Not that we can put that in the raws just yet, but it's the thought that counts.
A stone golem heated to stone-melting temperatures will have more mass than a stone-cold stone golem. Because energy has mass, and molten rock has more stored energy than just a rock.
Infinitesimal. One tonne of stone melted into magma would weigh like one tonne plus one billionth of a kilogram.
