Kaamash black

General comments: I got a bit more of your flavour here, which was nice.  I don’t know if there’s enough payoff for the ‘death matters’ theme.  Also I am not sure that I got a unified feel with the white cards.

Vile
Of course reminder text is shorthand, so I am imagining this to be short for “Spells that target ~ cost an additional 1 to cast.  Abilities that target ~ cost an additional 1 to activate.  Creatures can’t block ~ unless its controller pays 1.”  Note that this won’t work on triggered abilities.  Seems like a neat (if narrowish) combination evasion / defense ability.  The flavouring here is for black cards (which does restrict where you can use it), but the effects inherently are red/white (tax to block) and white/blue (tax to target).  The combination doesn’t feel generalisable enough to work as a keyword to me and would work better on a single card or a small cycle.

Spore tokens
I get what you’re going for by making some “death matters” cards and then some easy sacrifices.  I think that the result is a bit too cute and will confuse some readers.  It’s weird for the sake of being weird.  I think it would work better if there was a minor effect (gain 1 life for example) so that you don’t feel all bad.

End of Days
This plays into a couple spaces that Magic has dabbled in before – the ’10 life or less’ mechanic that Zendikar Vampires used a bit; and the ‘low life totals indicate the end times’ thing that Fateful Hour did.  Be very careful with effects that boost a creature’s toughness based on this effect – if combat damage lowers a player’s life total within range at the same time a creature receives lethal damage, the buff can save the creature in a way that will confuse players.  I am not sure about the “cut in half” wording – while I like scaling life total effects for non-20 formats, I don’t think this is necessary in every case.  ’10 life or less’ is probably fine here.

Beginning of the End
There’s no reason for these to be two separate paragraphs – can just be one.  It should also probably have the exile from hand being the creature’s controller rather than a potentially different player as otherwise it feels weird.

Assassin’s Strike was a strong uncommon; this is strictly better in three different ways.  Likely too strong for a common (also effect closely duplicated to Shattered Faith).  I’d probably bump it up or change it.

Black Market Soulthief
Wants ‘target creature an opponent controls’ to prevent situations where you either can’t cast it, or where you cast it and get caught out.

Bone Thief
MY BONES!

Hi there Deathgaze Cockatrice!

Burst Forth
The 0 in the textbox should be a mana symbol.  The quote in the last ability starts with an apostrophe and ends with a quotation mark – should be quotation marks both ends.

Council of Skulls
This sounds like a creature more than a spell.  If it’s advice, “counsel” is the right word.

Depraved Hedonist
“Human Horror” is weird.  The person is acting horrendously but the flavour doesn’t indicate to me that they’ve become merged with a Horror creature.  Giant Spider isn’t a Giant.

Card is fine though.

Elder Mindraker
Should be “that player” discards – see all Specters.

This is an unlikely effect to see at common – it’s never been done – but I could imagine it.

Obsidian Mindraker
The costs should be the other way around – T, Pay 1 life – as on fetchlands.

This is a second Mindraker – suggest you want this to be a species or group name for the Vampire Horrors, rather than a job they all have which is what it sounds like now.

The effect is neat though – a combination of milling and card selection.  There’s a cute teachable moment where I can see a card I want in my graveyard at end step and then leave it on top so I can mill it in my upkeep.

Offering of Blood
“Until end of turn, target creature gets +1/+0 for each creature that died this turn and gains indestructible.” – see Chorus of Might.

It’s weird that this is a combat trick that mostly doesn’t pump the creature despite saying it does.  Think it’s OK though.

Ohrmar Goons
“Indelicate” means tactless or indecent, which I’m pretty sure isn’t what you’re going for.

Mercenary has a whole bunch of crappy baggage attached to it that you may not want.

Neat vanilla dude.

Putrescent Panther
Is black’s theme “slapping Horror on everything”?

Nice design though – a death trigger incentivises you to get this into combat rather than creating too much of a standoff.

Retain Souls
“up to two target creature cards” – See Death’s Duet.

I really like cards that give you new resources and then mana to spend on them.  This is pretty strong.

Rotland Thugs
See earlier comments about toughness pumps and about Mercenaries.

This is the third return to the deathtouch well.  Suggest branching out into other black mechanics.  This card would play better if it took the ‘the game is ending’ bonus was a clean +2/+0.

Shattered Faith
Sip of Hemlock is a decent card and this is strictly better on two axes.  Black’s unconditional removal is usually the best common in the set or close to it and this is the second one.  You need to pick one.  This would be an excellent sorcery.

Shrieking Bloodhunters
No complaints here – a decently strong little creature.

Sole Survivor
Not sure about bringing back ‘Citizen’ but otherwise fine.

Soul Harvest
The flavour text makes no grammatical sense.  “Whatever the source was that replenished Kaamash’s mana had been, it faded long ago.”

Quite a lot of card advantage for a common.  Might end up at five.

Vile Roach
Three vanillas is probably too many.  The flavour here means I’d choose this one over the Rhinos.

Villianous Persuasion
Correct spelling is “Villainous”.

“That player discards that card.” – see Thoughtseize

Discard and draw is what Soul Harvest was doing.  Suggest upgrading to a Coercion instead.

Warp and Rot
“on target creature” – see Scar

Very similar to Burst Forth.  Essentially the same card.  Also another removal effect.