Yes, I think the average mana cost of the deck is huge. You have a one-drop accelerator, and then you have a bunch of 5 drops and onward (and Pristine Talisman, but that's a poor accelerator, and the lifegain is not relevant for the cost, so I'd just run Llanowar Elves in place of it, due to making colored mana), so you'd be torn to pieces before you could play a relevant spell. Sure, Sad Robot helps, but he does not make miracles (well, he kind of does, he draws cards, so he can trigger them). I'm not quite sure why you have Rootbound Crag (you can't be seriously expecting to run 1 of it, 1 wolf run, 1 Inkmoth and actually kill someone via poison, with Ghost Quarter looming around, even 1 of those screws your entire plan over sideways, and any instant-speed removal spell screws you as well), but I'd actually consider running the deck black/red and dropping the green. Since the demons cost a lot and your best spells are black anyway (except for Garruk, be he's really hard on your mana), I'd just swap green titans for Inferno Titan (gives a little breathing room against aggro decks when it comes down, as does Grave Titan), and use up the smaller slots that were supposed to be acceleration to run sweepers and direct damage spells, specialy the new one that exiles the creature, to get around undying, and Incinerates, since it kills Wolfir Avengers and Inkmoth Nexus. Also, some Doom Blades will be necessary, Restoration Angel and Wolfir Silverheart are coming in full force, so you could probably cut down on Tragic Slips, since you won't need to jump through hoops with Doom Blade, and burn is better at early kills anyway.
If you want to keep it BG, though, cut the cute Inkmoth plan and simply splash white for Lingering Souls, gives you better early game, doubles on Grim Backwoods for value, etc. And run Doom Blades. Also, consider Strangleroot Geist and Wolfir Avenger, since you have no blocking in the early game (Llanowar Elves will also help with these), and they might even doule up as pressure against slower decks.