I recently went through quite a bit of effort to survive obtaining a key (fire trap in explosive gas room...). After obtaining said key, I was walking though the only hallway back to the vault on the level, and it was full of "deadly lichen" that had not been there earlier.
I would like to get back to the vault - my potion of detect magic indicated that all the items inside the vault have benevolent magical auras. However, but I don't know how to get past this "deadly lichen", nor am I sure what's its effects on me might be.
To test the effects, I used my wand of beckoning to pull a kobold over onto the lichen, and it immediately became "fatally poisoned" and died within a few turns, so I've determined that walking over it seems like a BAD option.
So how can I get past the deadly lichen?
As a bonus, I'm also curious how deadly lichen forms if anyone knows. It was in the key room, so it may just be part of an elaborate key trap, but I haven't seen this before if that's the case, and it seems a little mean for a depth 3 key room.