Welcome to the Blue/Black Zombie deck guide!
Blue/Black Zombies: Purpose? To take other decks by storm! Remove their creatures, counter their spells, discard crucial cards all the while your zombies keep coming out and keep buffing each other!
To start off games, you want to try to cast a few Despise, Diregraf Ghoul or Gravecrawler. Getting early pressure out with one-drop creatures is important, keep in mind, these small itty-bitty creatures will eventually be big strong threats to the opponent. If you happen to get Quest for the Gravelord, put it out early so you can start sending out those 5/5 Zombie Giants!
With Despise you want to try and remove cheaper cost planeswalkers (3-4 drop) or cheaper cost creatures, (tap-for-mana elves and haste/dash creatures should be removed first). If the enemy ever starts playing high-cost creatures you can remove them efficiently with Go for the Throat.
Try to prevent the removal of your most important creatures, using Spell Pierce to deny the removal of your Diregraf Captain + Cemetery Reaper, they are both extremely important for buffing your other creatures. If you have Diregraf Captain and Gravecrawler on the field, you can attack with Gravecrawler as much as you want without worrying about trades, you can revive him immediately for 1 mana and the enemy will still lose one life due to Diregraf Captain's effect.
Keep in mind if a creature that you can't revive ever does die, you can use Cemetery Reaper to bring a 2/2 Zombie token onto the field, which will also receive buffs from your Diregraf Captain and Cemetery Reaper.
Your primary damage dealers should be Gravecrawler, Diregraf Ghoul and Geralf's Messenger, once they get buffed from Diregraf Captain and Cemetery Reaper you should be able to end the game quickly and without hesitation. Save your instant creature removal and counter spells for crucial moments in the game!
If you happen to get a Call to the Kindred you should be winning the game in a few turns, simply use Call to the Kindred to enchant one of your zombies and every upkeep you can play a free zombie creature without having to worry about mana. Eventually, this will lead to you getting Grimgrin, Corpse-Born and once he's on the battlefield, the game is pretty much over. Send out Grimgrin, Corpse-Born, sacrifice Gravecrawler to uptap Grimgrin and gain a +1/+1. (Note: If you have Diregraf Captain on the field, they will lose one life for the sacrifice of your Gravecrawler). Then you can revive your Gravecrawler for one mana and it's like you never lost any creatures!
You should save Spell Pierce for removal against your Grimgrin, Corpse-Born. Once he attacks, simply destroy the biggest threat on their team and repeat for infinite stacks on Grimgrin, your other buff creature should make this rather easy for you to wipe out the enemy in one or two turns once Grimgrin, Corpse-Born is out.
Game-winning Combo:
If you have Gravecrawler out and Grimgrin, Corpse-Born out you may sacrifice Gravecrawler to give Grimgrin +1/+1, then bring Gravecrawler back for one mana, repeat this process until you reach the desired power & toughness of Grimgrin.
Good luck and enjoy your zombies!
*oversized*