I've been refining this deck for months on Arena. I finally have it to a place where it wins consistently in open "Play" (BO1) format. Just recently, I won 10+ games in a row over 2 days in this format (typical games with this deck run 10+ minutes, btw). That said, it still cannot quite hold it's own in "Ranked" play (also BO1). My last foray in that format went 1-7. sigh
Despite all that, it's hella fun to play!!! I've had a number of long, drawn-out, back & forth battles where opponents will get me way down in life total, only for me to mount a comeback. For instance, one of my most recent battles with this deck featured an opponent who had over 50 life (playing an Orzhov Vampires deck) to my 13 life. Unfortunately, he played a combo that would have been the coup-de-grace for many (he played "Kaya's Wrath", followed by "Kaya, Orzhov Usurper", then exiled both copies of "Vraska's Contempt" from my graveyard). It actually played right into my hands as I played "Mulderhulk", followed my "Rhizome Lurcher" (which hit the board at 14/14) and "Sinister Sabotage" in my hand ready to counter anything game-changing he might try to play to defend himself. I have to point out that while I can often mount a comeback in these games, that doesn't always achieve the win, but you'll have a seriously fun time playing it out!
My strategy is to use "Stitcher's Supplier" and "Wall of Lost Thoughts" early in the game (heck, at ANY point of the game) to load the graveyard and cycle through cards faster. "Severed Strands" and "Ravenous Harpy" also help flesh out the graveyard a bit sacrificially. Then simply let the rest of the deck take it from there! It's extremely satisfying to play "Lotleth Giant" to do a large sum of damage, have your opponent kill it, simply to bring it back the next turn and hit them for even more damage than the last turn! Once you get "Muldrotha, the Gravetide" out, the REAL fun starts to kick in. Even if your opponent manages to kill Muldrotha, just bring it back! (there are a number of other cards with "return from graveyard" abilities to cover for you in case Muldrotha isn't in play or gets eliminated). To be honest, since there's only 1 copy of Muldrotha in the deck, it doesn't often see the board anyway, but this deck holds its own without it.
EDIT
(04/19/19) Just got a copy of "Underrealm Lich" in Arena, so I've added that to the deck. Haven't played it yet to see how well it fits in, though...
The deck is weak against fast decks with good power ramp. It's also susceptible to getting important cards exiled. I haven't gone up against many "Control" decks (featuring Dovin, Jace, or Teferi). It does so-so against Mill decks because, well, the deck is designed to partially mill itself. So as you can imagine, unless "The Gravetide" deck starts doing its business quickly, you're only speeding up the Mill deck's process.
