Hey,
first of all my common mantra about the land base: "if it always enters tapped, it needs to have a significant effect".
Obelisk of Grixis could be replaced with Darksteel Ignot. Same cmc and effect, but the Ignot is indestructible.
Fellwar Stone and
Exotic Orchard could also do a good job for colorfixing.
Besides that, the deck is lacking
Nicol Bolas.
I would also reccomend to think about the amass and draw damage mechanics. The former doesn't seem strong enough for me and the latter could result in more problems than it solves. Especially for combo decks it can be extremly
dangerous to offer them some additional card draw, even if you let them discard the cards afterwards.