It was Ling, who has been turned into Greed. At this point, I wasn't sure he was going to come back to Ed's side. The fact that he hasn't been seen for like, 10 episodes doesn't help either. But it shows him fighting Wrath and Envy which kinda tells me that he is going to regain control at some point ruining that future plotline. Because in the previous opening theme animation(FMA:B seems to have a new one every 12 episodes or so) it shows Greed with the rest of the Homoculi(technincally before he becomes one because he doesn't become one until that episode where they changed the opening animation, but it's kinda hard to tell that it is actually Ling).
Also, Ed and Al and the gang have teamed up with Scar for the time being and they have also got a few chimeras on their team as well. Now, before I even knew they were chimeras, the end credits shows all of the badguys really quickly, then it shows the good guys jumping up in the air starting with Ed and Al and it goes down the line of the rest of the good guys...then it shows the chimeras that are still considered bad for a few more episodes with the good guys meaning "hey, they will become semi major characters on Ed and Al's side! Thanks for ruining that!".