To me, I think you should add in your side board a Nihil Spellbomb, incase a card that reshuffle their deck is your opponent.
Another suggestion is add Mindbreak Trap. Just in case there is some things that should NOT goes into the graveyard.


Thats all I can think of for now.

I'd say personally either remove Keening Stone or Contagion Engine and put in more of whichever you keep. The thing is, They're both your endgame drops that are intended on sucking up your mana. But if you have both out, one of them is going to be sitting there useless, while the other does things. And you might want to splash white so that you have some Remove from Play cards since Eldrazis kind of destroy your strategy.