Just a few comments:1. What do you plan on sacrificing with Ashnod's Altar? Only Skittering Invasion, Spawning Bed, and Blight Herder put sacrificable creatures on the board, or you'd have to sacrifice the big ones for just 2 mana... Same goes for Eldrazi Monument by the way.
For the mana you could take a look at Blinkmoth Urn, although it may also give mana to your opponents.
2. Gruesome Slaughter sounds fun, but at which point would you actually use it? Half of your creatures seem to have Annihilator, some are so weak that the extra ability won't help, and with a 10/10 you'd probably want to swing face instead of dealing 10 to a creature "for free". Maybe Akroma's Memorial fits better if you plan to have this kind of effect.
3. Which artifacts do you plan to sacrifice with Phyrexia's Core? Otherwise it would just be as good as a Wastes (see point 4).
4. Ash Barrens, Cloudpost, and Holdout Settlement seem to add nothing more than a Wastes would do. While they may look nicer, with more Wastes you could also consider running Solemn Simulacrum and Burnished Hart.
5. You are severely lacking card draw. Consider a Mind's Eye or a Sandstone Oracle.

Justist, thank you so much for the feedback!

ok so the reason I thought Ashnod's Altar would be useful is if someone tried to steal an eldrazi, it's a quick way to sac and dodge a potential beat down.

otherwise, this deck was put together with what I had, so yes a few lands def need to be changed out. good point.

also, I was eyeing up Akroma's Memorial recently, it would be worlds better.

again, thanks for all the feedback :-)