Basically the only thing you need on the back of the upper legs is something that makes them look not too bare. So you could maybe try adding System pieces with their knobs to connect them to the pinholes.
Light grey CCBS bones probably wouldn't work too well due to the colour.
Depends on if I'm asked for help or not
I would advise you take a little more time before posting updates, though. From experiecne I can say that sometimes it works best to build something and look at it again a day later to fix issues by yourself. Always ask yourself these questions before posting anything: Do I really like this? What could be improved and how? Only when the answers are "Yes" and "Currently nothing" is a MOC ready to be posted.
By toying around with parts and finding solutions you learn a lot of useful MOCing techniques and by critically looking at your own MOC you learn to improve.
In the end it matters most that you like the MOC, not me. All that matters for me in the end is if I can see that some serious work and consideration was put into building the MOC.
I'm happy to help whenever I can, but I think you should try working with your own ideas a bit more before you ask for specific opinions of how else to improve.
I mean, I consider myself fairly quick at building a whole new MOC - but that still usually takes one to two weeks minimum.
Aaand I see you've just updated him again...
- light grey upper legs aren't as bad as I thought, but you need bigger CCBS armor for the longer pieces
- wrists look bad - simply go for the very first lower arm design and put a balljoint at its end and you have a streight arm with wrist articulation
- cable could still be better integrated, but it's an improvement
- chains are a nice inclusion
... Hm, you know what? I think you should return everything except the lower legs and the torso to its original shape. Then you get wrist articulation in there. Then you try filling in the torso a bit more if you can. And then you wait a few days and think about what else can be improved and do that.
Not particularly fond of it, honestly. It's just kinda weird. As far as canon lore goes there's admittedly nothing wrong with it so far, but
This all just doesn't make much sense to me.
a) Friendship and trust aren't exactly things Makuta are known for
b) No one saw it coming that Teridax was up to seizing control of the Brotherhood - the Convocation was a big surprise to most, I'd say
c) Befriending Gorast is just a thing that would not happen