5. Melisandre And The Brotherhood
This is something that simplifies the original material while at the same time taking advantage of untapped character possibilities. In the books, Melisandre never goes to see the Brotherhood. There is another one of Robert Baratheons b**tards much closer, and he ends up suiting Melisandres needs. Gendry goes off with the Brotherhood. He pops up again in the fourth book, more in a Oh hey, cool! way than a necessary one. By bringing Melisandre to Dondarrion and his men, an unremarkable character is entirely eliminated and a character with great potential gets more development. Also, having our two Red Priests interact strengthens the mythos of the Lord of Light.