I like the changes you have made to your decklist
I think the focus on +1/+1 counters is gonna be fun
Some observations so far:
Corpsejack Menace should be bumped up to 4, or 3, if you consistently want the ability to double +1/+1 counters.
You should add some kind of spell to "feed" your graveyard and find the creatures you want to cast. Don't be worried about doing that either, Your graveyard is a resource in a deck like this so you want it to be stocked.
Soulflayer wants you to
exile creature cards from your graveyard to make it cheaper to cast and gain extra abilities so you will need creatures in your graveyard to
exile.
Grisly Salvage or
Gather the Pack will do that for you. You find 1 or 2 creatures you want and put the rest of the cards in your graveyard for use later either from
Soulflayer or
Varolz, the Scar-Striped.
You have a lot of creatures that have high power like
Outland Colossus or will get high power from +1/+1 counters and you don't have much in the way of evasion abilities like flying, trample, unblockable, ect.... Basically you have a lot of damage potential and no way to make sure it gets through.
Outland colossus can be chump blocked by 1/1's every combat the same is true for most of your creatures. Maybe add some cards like
Predator's Strike,
Overrun,
Evolution Charm, or
Tread Upon to give your creatures the ability to get damage through and kill your opponent.
Also I would consider looking at more reliable removal options.
Tragic Slip is a great card (I own a playset myself) but it does require something to die before it does -13/-13 so it can be unreliable, when you need something to die Morbid might not be activated. Its better to focus on spells like
Doom Blade,
Putrefy,
Go For the Throat, or
Ultimate Price.
Tragic Slip works well with those cards too... Destroy a creature and trigger Morbid then
Tragic Slip something else
In general it is better to focus on more copies of fewer cards then it is to have lots of cards but only 1 or 2 copies of them. When I start building a deck I find 9 or 10 cards that work together to achieve the goal of the deck, how I want to win, and I put 3 or 4 copies of that card into the deck. Then I run some test hands with proxies, or on this site using the Starting Hand and Draw a card options, to see what the deck will look like as I "play" a game. Then I fine tune by identifying the weaknesses of the deck and changing what doesn't work.
I hope this helps you out