How do you do that? I've read you can summon the guy you can talk to before the bridge but you need to be human? I did have 5 humanity stones but have used them all regenerating energy v Gargoyles. Although using the humanity stone doesnt seem to change me to human i still look like death?
Seems a bit crazy that the game is a single player but you need to do boss battles in co-op mode.
might be a bit late now seeing as you posted this 3 weeks ago
you can farm humanity by killing rats, best place if you've opened it up is the sewers in the depths, from the bonfire there's about 18 rats you can kill in a run that'll take you 3 or 4 minutes
if not you can kill the 3 rats in the room under the bridge with the dragon on it then run back to the bonfire at ther bottom of the ladder to respawn them, you'll not farm loads in this area but it's useful to keep some on you so you can revive & summon a npc/another player before boss fights
if you consume humanity it'll raise your item discovery, the default rating with 0 humanity is 100 and you can increase it up to 210 by consuming 15 humanity (with the covetous gold serpent ring equipped you can raise it to 410) it also raises curse resistance and your defense stats
to become human consume 1 humanity then rest at a bonfire and select reverse hollowing, just note that in human form other players can invade your game
you don't need to do boss battles in co-op mode, it's just an option to help you out if you get stuck much like in demon's souls where you could summon other players or some of the npc's would help you out if you triggered certain events