You should try and limit your deck to 40 cards, it increases the chance of you drawing a specific card that you want.
One of the best cards I have found is Tombe of the Dead, I mulligan for it in almost every matchup. If you can place it down on turn 3, it will wipe the board at the end of turn 6. Perfect for a Hekeem turn 7. Tombe places all characters in play into your graveyard, so you'll often get some of the enemies characters coming out too. This should be more than enough to win before Calamity becomes relevant.
The card Fear combos extremely well with Tombe, helping you stall those last few tombe turns.
Boomy is also very good at stalling, especially against Flame Dawn decks.
I know you probably don't have all the cards, but Undeath Wish is a very versatile card that can be used either as removal or for reviving Hekheem. I would recommend trying to get 3 of these.
Plaguebearer and Bloodfirsty Dead are great 2 drops, I recommend using 3 of each in your deck.
If you have 3 Hekeems I would recommend using Hekeem in deck and not using it in command, as its very easy for your opponent to remove Hekeem with something like a Vererorian Kidnapper and ruining your strategy.
Patient Zero is not a very good card, I recommend using something else in command like Zombie Scavenger.
Cards you could add:
- Tombe of the Dead
- More bloofirsty deads
- More plaguebearers
Cards you could remove:
- Sleeper of Averach
- Risen of Averach
- Infected Pack leader
- Averach has risen
- Infectious Zombie