At first glance, Molderhulk doesn't seem like he does much. It's a big setup and cost for a relatively unimpactful EtB effect and a body that a lot of other green decks can get onto the board with a lot less setup. However, persistent cost reduction on a commander is an underappreciated thing of beauty. Only a few commanders in regular EDH have this same quality (for example, Ghalta, Primal Hunger and Karador, Ghost Chieftain), and most of those owe a lot of their flexibility to that cost reduction. While we can't take advantage of repeatedly playing our commander for cheap in the same broken ways in PDH, when the reduction is tied to a body of a decent size, you end up with this weird form of card advantage. The enemy will keep having to use cards to remove Molderhulk, or they'll have to let creatures die to trade with it. If you can just keep replaying your hulk for GB each time, you'll quickly find yourself with cards in hand while your opponents are running out of gas.
The gameplan of this deck comes in three stages, usually. First, you play all the ramp, cycling, and mill effects you have in your oppening 10 or 11 cards. This sets you up to play Molderhulk, sometimes as early as turn 5. Oftentimes, he is the biggest thing on the board when he hits, so he'll get removed. That's fine, because stage 2 is all about letting your opponents use up their removal while you replay Molderhulk, ramp up using his EtB ability, continue milling, and slip out a few utility creatures like Undertaker or Nightshade Peddler. You can also do nasty things like wipe the board with Crypt Rats at this point to set your opponents WAY back. Stage 3 is when you get Molderhulk to stick around and have also filled up your grave a bit more. Now you're ready to start playing bigger beaters like Undergrowth Scavenger and Rhizome Lurcher. You can also use things like Vigorspore Wurm for a surprise kill by buffing a flier or creature with trample. If you have Opal Palace at this point, you should also be able to make your commander huge, like a 10/10. Basically you've done most of your black-aligned stuff in the first two-thirds of the game, and now the green in the deck can REALLY kick in to finish your opponents off.
Most of the deck is pretty straight forward, but there are a few points I would like to stress. First, keeping the creature count as high as it is will be VITAL to this deck, as reducing your creature count makes your mill effects put fewer bodies into your graveyard, causing you to wait an additional turn or two to play Molderhulk. If this happens, you're just going to feel behind and ineffective the whole game. Second, this deck runs the fewest basics out of any deck I have made yet. That's because Molderhulk is an excellent engine for reusing lands that you have either cycled or sacrificed. This allows you to do things like use Haunted Fengraf to resurrect multiple creatures, or tutor a ton of the lands out of your deck with Evolving Wilds so that you're more likely to draw useful cards. Lastly, there is a useful combo in here for recurring whatever creatures you want out of your graveyard in a long game. Undertaker will allow your to discard Sanitarium Skeleton while putting a creature from your grave back into your hand. Then you can pay to put Sanitarium Skeleton back in your hand to rinse and repeat. This means that for 2BB, you can return one creature to hand each turn.
Areas of flexibility are that I could see a little bit more of an aristocrats theme, or you could use just a few more spells with flashback/recover/retrace. The aristocrats theme (saccing creatures to buff other creatures) would give the deck a bit stronger of a defense against Pacifism and Arrest cards, since you can sac creatures out from under the auras. Right now those auras are pretty good at locking down our commander. The flashback/recover/retrace cards are just going make the deck appeal to people who don't like having every single ability in the deck attached to a body, while still working with the self-mill theme.
The major glaring weakness of this deck is that a single Bojuka Bog or other piece of grave hate will absolutely wreck it. So long as that's a risk you're willing to take, this is a great deck that has felt like a strong contender every time I have played it.
