I've been playing on the Arena ladder with quite a few of my own iterations on a Golgari deck, and this is the one I'm most happiest with at the moment. 

With my other deck here I found that glowspore shaman was my favourite creature to have out, and whenever I would draw an orzhov enforcer or priest of forgotten gods it wouldn't feel great because they both only have 1 power. Playing gutterbones into shaman into midnight reaper is a really powerful curve, and I wanted to have more of those sorts of plays and so decided to include more 3 power creatures, with only seekers' squire being slightly weaker for its better defensive stats and utility. 

I'd call this an aggro-midrange deck. It seems to work quite well against a number of match-ups, although it struggles against go-wide strategies if you don't draw lots of your removal and against control strategies if you aren't able to land a midnight reaper or a vraska for the card draw.

Some notable cards:

"Necrotic Wound" - This card is absolutely amazing and I reckon if you're going to do anything with the 'undergrowth' mechanic then it ought to be a four-of in your deck. It's that good. You only need one creature in the graveyard for it to exile pteramanders, tithe takers, runaway steamkins, and so on, and every additional creature in the bin just makes it better and better until eventually you're just exiling gate collosuses (collosi) with a -13/-13 one mana instant speed exile effect. Rekindling phoenixes stand no chance at all, Lyra Dawnbringers swoop in to block your creatures only to be removed for one mana... so good.

"Vraska, Golgari Queen" - Not a very popular planeswalker it seems, but I've found it's actually very well positioned in the meta. The +2 lets you sac creatures with midnight reaper out to draw 2 cards for zero life loss, or it lets you just tap a land for its mana, sac the land, then play whatever you draw, which in a deck that basically tops out at 4 mana is quite a useful way to use unwanted land draws to dig for creatures - plus, the 1 life it can give you every turn is also not irrelevant. The -3 kills every single creature in both mono-red and in mono-blue, and it also kills benalish marshals in mono-white. Against the gates deck it kills both gatebreaker ram and their guild summits, destroying their card draw engine. The ultimate also wins plenty of games once you exhaust all of your opponent's resources and can just sit back and defend her until you get the emblem.

"Journey to Eternity" - This card is great fun, although you need to know when to time using it as it's not really something you can use willy-nilly. Against aggro decks it's best to throw it onto one of your weaker blockers that you're intending to trade off to make them not want to attack, and against control it's best used when you've got them on the back foot with several creatures on the board: you put it on one of your many 3-power creatures and they're forced into the situation where they can either wrath the board and flip it for you, or vraska's contempt the creature with the journey but then take a bunch of damage from all the other creatures you have. Either one is good for you.

The only time I've played journey on curve is against the gates deck where you go gutterbones, shaman, journey on the shaman. The five damage a turn tends to force them to cast gates ablaze immediately, but that flips your journey, ramps you, brings back your attacker, and sets you up for instant speed shenanigans for the rest of the game. If they don't gates ablaze you then you just hit them for 5 and play midnight reaper, and then they're really screwed.

"Izoni, Thousand-Eyed" - This is a "fun-of", although it has won me quite a few games so I dunno. It works well as the card you keep bringing back using Atzal, cave of eternity, but probably 'Golgari Raiders' would work better as a finisher. This deck could use some more direct undergrowth payoffs most likely, but all you've really got is Izoni, raiders, and molderhulk... hmm.

"Kraul Harpooner" - This is already recognized as a great card in general, but it's at its best in an actual undergrowth deck. Kills Nicol Bolas in Grixis match-ups, kills doom whisperers, eats the flyers in mono-blue and white, etc.

"Glowspore Shaman" - The more I play this card the more I like it. It's a great attacker against midrange and control, and unless your opponent has a goblin chainwhirler it's also a great blocker. The ability is useful not only for filling your graveyard but also to find land since it gives you three chances to hit one, and if you don't need the land? You just decline the ability. A lot of other undergrowth decks I've seen have this /and/ 'stitcher's supplier' in order to go all-in on undergrowth, but stitcher's supplier is a bad creature with only one function, whereas glowspore shaman is a fine creature with a strong ability that finds you land too. I've found that four glowspore shamans is all you need to enable undergrowth reliably without sacrificing the quality of creatures in the deck.

"Thrashing Brontodon" - This is another universally-recognised good creature, but there's a fun interaction with journey to eternity. If you have a brontodon out, you can enchant it with journey and then pay 1 mana to use brontodon's ability targeting the journey it's enchanted with. Brontodon gets sacrificed as part of the cost which immediately flips journey, and then the ability simply fizzles because it no longer has a target - you still get your brontodon back, but now you have a flipped journey completely out of nowhere. You can also do the same thing targeting one of your opponent's enchantments (or artifacts), but it's one more option alongside Vraska when it comes to sacrificing the creatures you enchant with journey.