Why be summoned as mound-makers if not fighting?

Was farming for vertebrae in the catacombs. There was a pink summon sign for mad-spirit. So I summoned. I assumed this person also was possibly farming vertebrae, so I'd help by letting myself get killed. But the spirit just emoted and took off armor and such, but did not attack. I did attack eventually and got nothing.

I summoned a few more times and only once was I attacked, and once I actually used a trap to kill myself while the spirit used an ember.

So... what is this person doing? Why be summoned and then do nothing? Is the spirit trying to help with a boss?