As the proud owner of a yagron deck, I've been playing around with it recently and its finally starting to grow on me. That said there are a few things here I don't quite understand.
Black Bind Witch
I'll admit to being biased here as I typically don't like anything below 4 hp in the command zone, but I really don't understand why you have her here she's way too easy to stop in the command and honestly you lose 2 cards to stop one opposing card. Aside from dealing with Gao Han, this card actually puts you at a deficit just by playing it. Chances are if your opponent sees this right off the bat they aren't going to impale anything worth killing on it.
If you're going to use this card you absolutely need to have ways to handle it in the event its killed. Personally I go with demonize, descent into madness or even your death ray could work. I think this one is more of a personal taste, but in early game he can cause such wide tempo swings both for you and against you that I'm not a big fan of using him in a deck where I'm generating only slightly less powerful 8/8 creatures almost every single turn.
Demon of Solitude
If you had more discard power I could completely understand using him. That said, he's going to spend most of the game pretty weak since Yagron tends to flood your hand around the time the 3-5 creatures come down. To be honest, this deck really doesn't have the discard power to make him viable.
Agent Coyle, Superior Symbiote
The cheapest thing your going to get back is a 3 cost master of demons. In my personal experience with Yagron, this is something that you really can't afford with him. Have you considered trying adaptive ritualist instead? You have to remove a card from the game, but you get something out of your graveyard at cost AND get a nice 8/8 creature to boot.
In most decks this card is great. However, exiles are definitely not most decks. I'd swap this out for demonic presence. Getting a 5 card refresh and being able to discard your whole hand, while more expensive gives you more options with exiles.