Thanks Finn (Almost called you Fenn)

Some of my points may not be as old was GRAAL will be, so I hope no GRAAL roleplayers won't attack me or use them in the stories if they don't happen yet.

Here are some other correlation that I will briefly compare:

Quest:
In the Spoils of Annwfn, King Arthur went on a search for the cauldron while in Branwen Daughter of Llyr, Bran went on a search for the cauldron. Arthur lost all but 7 men, so did Bran.

Druids/Merlin: (Latest to earlest mention)
Lailoken, runs away and learns to tell future, Myrddin learns to tell future, Merlin can tell future. Notice the similarity in names between Merlin and Myrddin.

Rituals:

Excalibur is thrown into the lake - Celts threw weapons into lake as offerings.