Tomb of the Spirit Dragon is an absolute necessity in any eldrazi deck right now. Especially if you're running cheap aggro creatures... The health you can gain in one turn in the mid-late game of standard is literally unbalanced. Other than that I would recommend looking at cards like Kozilek's Return, Oblivion Strike, Titan's Presence, Sifter of Skulls, Dread Defiler, Deathless Behemoth, Endless One.

In terms of Bearer of Silence, I have it in a Sultai deck that utilizes it primarily as a removal spell. With the other cards I listed you can keep it in your hand as a sneaky ninja waiting to remove their big threat before becoming like a mosquito that hits without resistance for 2 every turn.

In the last version of this deck, I was curving out every turn. In that build, Tomb of the Spirit Dragon is useless because its net worth is about 3 life per game, towards the end game. Which isn't worth it. I'll play around with it in this build but I think it'll be a somewhat similar experience. In response to the rest of the cards you mentioned, Kozilek's Return Kills all my creatures except for 3. Wouldn't play that mainboard. Maybe a SB option. I don't like Oblivion Strike. I feel it's too expensive and if I would rather play more copies of Thought-Knot Seer but I don't want more of those either. Titan's Presence I will consider for SB. I would play Sifter of Skulls if it also counted when it dies, which sadly it doesn't. Dread Defiler is WAY out of my mana curve. With this deck, by the time that turn comes around one of us should be dead. IF I can get to that amount of mana, I still wouldn't play it. Too expensive. I don't like Deathless Behemoth. I don't even draft it. I have better things to spend my mana on. I had Endless One in a previous version of this deck. It really doesn't put enough pressure on my opponent. Especially after I pump it full of mana, it just typically gets exiled. As for Bearer of Silence, I thought of it that way for a while as well. But it can't force my opponent to choose their threat to sac, so it's not as useful. Here's an example, Elf deck: sac a token. No worries. Rally deck: sac anything but Jace, (which is helping them) and possible Zulaport Cutthroat trigger. Any token/scion producing deck just sacs a token. Against a control match-up I would probably bring it in, but other than that, there are better ways to remove things. Which is why I'm now playing Grasp of Darkness and Spatial Contortion. Whew. I'll play around with the two I was unsure about. Thank you for the suggestions!