Sozac said:
I don't get what makes Gwyndolin evil. I get that he made an illusion of his sister because she left, but I don't know why. Also, the illusion sticks around after I kill him which is weird. However, he seems intent on me not coming into that tomb which just gives him a role as protector. I'm sure I am missing something because I wasn't searching for it. I don't ever read weapon descriptions. I know I killed Havel and I have his ring and armor, but I don't know who he is. Also, I never met onionhead again and it says he is from another land. Was that land where Demon Souls took place.
While I can't tell you where Catarina is, I can help you with Seigmeyer.
You first encounter him waiting to enter Sen's Fortress. You then meet him contemplating how to wipe out a bunch of Silver Knights in Anor Lando.You must talk to him before, and after clearing the room.
You then will most likely encounter him before his daughter in Blight Town in front of the entrance to the great hollow. He needs three purple moss clumps.
You will encounter his daughter, Seiglind in a golden crystal monster outside the Duke's Archives on the way to kill Seathe.
Then you will see her at Firelink Shrine.
You then encounter Seigmeyer in Lost Izalith, where he pledges to save you from the "Will it blend?" demons. If you kill them before he attacks, you end the story. If you let him get below 50% HP, he dies and you end the story. If you save him, you go back to the bon fire at the start of Ash Lake to see the ending.
The game is rich in wonderful story, and it's hard to find sometimes, but this was my second favorite arc. First being how much of a dick you are for killing Quelaag.