Furor of the Bitten over Guise of Fire, unless you plan to use Guise of Fire for removal a lot.
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Maybe Cliffrunner Behemoth over Obstinate Baloth, since it can be summoned by Mayael and can potentially gain a lot more then 4 life.
Not sure how Purphoros or Hammer would help considering you would never have 5 devotion and you don't need haste on creatures and you would be lucky to hit enough lands to use hammer active.
Undying evil could be another possible option, depending on how much black you want to have
Really, because I believe it is legal in Modern
Omnath, Locus of Mana would be great also
Well you have Lightning Strike in Theros so there is your Searing Spear
Thanks, look into this
Breaking and Entering and Mind Funeral could be good dimer cards if you move in that direction a little move.
If you are looking for just a zombie to sacrifice, I think Butcher Ghoul could be better because you could sac it twice before having to use ghoulcallers chant. Another card that have more valve when sacrificing could be something like festering newt that could also take down another creature or just weaken it for a turn when you do sac it.
Because, you are missing both Blur Silver and Thorncaster sliver, much better cards for a Silver deck.
Interesting Morbid Deck and I understand why you are keeping it cheap, but why Gutter Skulk? Lots of other good 2 drops that have low cost and are WAY better.
I am a little confused on why Feral Animist, Skarrg Guildmage and Awaken the Ancient are in the deck? I understand that the Guildmage and Awaken are both strong cards, they just don't seem to fit the deck.