Dark Plans, Part I:
The Goblin Lady is the simplest of your nemeses to explain, as she has little knowledge of the other, larger enemy, though her threat was more immediately powerful.
I had toyed with the idea of making her Morgan la Fey, not sure whether giving Morgan such an overt role in opposing Arthur would be more damaging to the genre than inventing yet another villain. In the end, I decided that since I already had Judas Iscariot in a minor role, and the Predicant, that it wouldn't hurt to add to the canon one more time. Therefore, The Goblin Lady was an entirely new villain.
The Goblin lady is a powerful enchantress who hates Arthur. I never really worked out a reason why, but it never came up, so it matters little. Probably the best reason I'd eventually have had to come up with would be to make her a representative of the Foul Folk: those who dissented from the Faerie and work against it. Most of them are goblins, but still.
The Goblin Lady actually had two plans working at the same time. First, she feared that Arthur and the kingdom of the Faerie Grove would strike an alliance, so she began inciting the traditional enemies of the Faerie: the Goblins. (this is where she got her name, which I gave to her mostly as a placeholder, since she was y'know, the one beind the goblin attacks). As the second prong of this plan, she began poisoning the Faerie Grove using spells and demonic summonings. Ultimately, this meant bringing a demon into the world, but she wasn't thinking that far ahead.
When it seemed the time was right, she wanted to use these goblins against Camelot, but she wanted to weaken Arthur's forces first, so she took a page out of the "Knight Errant Generic Enemy Plans" book and established a plan she hoped would pull knights away a few at a time and they could be more easily disposed of. To this end, she got two of her thralls, a dwarf named Rupert and a diminutive illusionist named Rowena, to trick a knight or two at a time away from Arthurs court with a phoney story about a damsel in distress. Only Rupert wasn't going along with it very well, since he was only kept in line by fear. So Rowena had to abandon the party to help prepare for their arrival.
This "pull the knights away" plan was abandoned when, due to the unexpected onset of war with Lucius, there were a) not very many knights in Britain anyway, and b) even if there were, they woulnd't be hanging out in camelot waiting for random adventures.
The second plan is a bit more hazy and well, represents some admittedly weaker plotting on my part. The idea is that this plan was going to be forsaken as well, since there was little need to distract the Knights of the Round Table, but then the Goblin Lady encountered more resistance than she expected (primarily in the form of PCs, and some commoners) she decided to continue with it to weaken the world.
The Goblin Lady had captured the Questing Beast, and through a sick, dark age version of Dr. Moreau style genetic work, had bred it with dragons. The results were dragons that lived life much faster than things around it (in mechanics terms, they were permanently Hasted) but also aged much faster and ended up rotting from the inside out. This is what Cadamis and Providian and their group found after the ritual Cadamis performed at the well. Hatchling versions are what killed off half the PCs when I culled the ranks. The dragons spread too quickly, however, and a group of the PCs managed to (accidentally) release the Questing Beast (due to Sir Pellinore's interferance), so the plan wasn't as effective as she wanted. Especially since the dragons were spreading further than she intended, and weren't concentrated enough to be effective. Thus I was going ot be able to throw red, green, white, blue, and black dragons at the players as they travelled. But we didn't get to most of that. So sad.
So, what was this I said about the Demon? Sorry, you'll have to wait for a future update on that. Next up, some more revelations about the Faerie.