Vulturous Zombie. At five mana, it's expensive and it needs other cards in order to get going. However, it's the deck's only flier and it has the potential to get really big but now it's hugely matchup dependent. The creature has to survive and something has to go to an opponent's graveyard and I can't always make that happen rapidly.
For example, in this matchup against a Pox deck, there was just too much removal for me to get anything going. Did I get a VZ out? Yes. Did it die almost immediately? Also yes. With +1 counters on it.
I did win the match, though: my opponent had mana issues, flooding out at inopportune times and in game 3 choosing to discard a Pox to his cast Pox, giving me a chance to recover.
In another mono black matchup, this one focused on heavy discard and flying creatures, Hurricane was my best friend, as was trying to play the deck out as fast as I could. I think I lost the matchup but it was a close one. Pernicious Deed was, as always, a rockstar.
I also got some games against a mono-blue deck and was fortunate enough to see Sword of Fire and Ice in those games and I'm pretty sure you can imagine how those went.|
Finally, I had an interesting match against Birthing Pod, piloted by Noah. A pretty solid series of games, (despite me losing) where VZ was good, a card that he didn't want to see, and even won me a game because it couldn't be blocked, it was also just a 3/3 for 5 that I had to do things to in order for it to be great.
So I can't say that the Zombie has been great. Something else may be required and I'll have to dig into what, though I'm lacking ideas right now.
On the upside, the Reaper of the Wilds has been wonderful: a great threat with useful abilities, so that's been a good change.