No, I did not submit my soul to the will of the rat. Also I wasn't invaded down there. I did get invaded each time I went to one of they Belfry's however. I was in the knights of blue covenant for a while but never could connect to a world of a sinner, hence I forgot about it after a while and am now a follower of sunlight and hence praise the sun \o/
I guess all fights can be done solo, but especially those with multiple enemies get of course much easier once you have someone else is in the room. Also, summoning another sunbro gives me a sunlight medal I need for leveling up my covenant, hence it's a good idea for me to summon them anyway.
Levels: I'm now already SL 130ish... which by old Dark Souls standards is outrageously high. I think I was SL120 at the end of my NG+ in the first game? I don't feel as powerful as with SL120 in the old game however, so I guess the new SL are just not as strong. But SL alone is meaningless anyway, the equipment is very important after all and I think it's a good idea from FromSoft that they now don't take SL as metric for PvP and Co-Op but collected souls. It seems to work in that sense that with every invader so far I got the feeling we're at about the same level, while I was usually utterly destroyed by invaders in the first game. I beat about 50% of invaders, which in my book counts as good matchmaking.
Shrine of Winter is one of the doors you can't pass in the shaded woods, yes.
Lorewise there is a lot of interesting stuff going on, for example that the Lost Sinner tried to use the soul of the Witch of Izalith to reignite the first flame. Uhm... isn't that the soul you collect as player in the first game?
So she must have been around since the times of Lordran, like other heroes and villains of that era tried to reignite the flames or usher in the age of humans, the age of darkness. She failed to reignite the flames, perhaps due to inaction after facing Gwyn, and been locked away ever since.
What equipment made the Lost Sinner easy for you? For me it was having a 100% block shield
I was fighting her in darkness as well since I found the keys much later.
I'm now facing King Vendrick. Something is wrong here, I tried him a couple of times but don't seem to do damage. Only bleed seems to do a little, I guess I'm missing something or should do something else before coming back to him. Maybe some item that I need? So I ventured to the East, through something like a laboratory or museum, still not sure. I also ran into an old friend. Had to kill her.