After a fair bit of time playing around, I find Gravity/Water Otyugh+SoPa core decks to be the most consistent at beating Platinum Arena, even more so than SoSac decks (especially since the AI got smarter). It can usually get you a special spin (2 consecutive wins) every 6-7 games and beats False God about 50% of the time.
This deck is by no means original, but it only appears in the arena on occasion.
Below is the variant I am running. See sections afterwards for substitutes/other options.
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Card Options and Upgrade OrderEdit
Otyughs are a must. I would not suggest running any fewer than 5. I used to run 4, but too often you don't get one in the opening and get rushed down.
Shard of patience is obviously a must. I find 4 to be a good balance; 3 may be viable.
Shard of Focus is the next key part of the deck. The deck gets a lot less versatile without it - you get fairly easily beaten by shields, your chances against Shard of Freedom based decks fall dramatically, and it becomes a lot harder to beat Discord/Black Hole (which this deck is very good at doing - but it seems the metagame has evolved so you don't see that archetype much anymore). You may be able to substitute chargers if you don't have the shards, though I haven't tested how well this will work.
Gravity Force is to save yourself from rushdown, and can be useful in a pinch to take down overly buffed monsters. I used to run 2; choice is up to you. Remove if you don't have Shard of Focus.
Gravity Nymph is nice for the healing factor, and also for destroying certain decks if you get it out early. I only have 1 - I think running anywhere from 0 to 2 would work fine. If running 0, maybe best to run 2 gravity force.
Pillars - I suggest 15 (perhaps more if unupgraded). This deck needs to be able to get otyugh on turn 2, and it is actually quite quanta heavy.
This deck destroys Mono-Dark and most Devourer-variant decks. As I write, I was the only one to beat Amy Guo's Devourer/Earthquake arena deck out of over 30 who tried. I almost never lose to mono-dark decks.
On the flipside, I always lose to well-built mono-aether decks. You might think the deck would do well with the shards of focus, but you get rushed down too quickly (with no way to stop the spell damage). Lobotomizer before you get shard of focus out also means an instant surrender.
I usually lose to poison variants as well. Light/death, mono death, death/water, etc. are all hard for this deck. You can consider running purify, but I don't see enough poison to justify it.
Light/Fire, etc. - this deck loses if the stall deck has too much control (ie rage elixirs, fire bolts), but usually wins against those that just spam healing effects. Will lose to rainbow control decks based on pandaemonium.
Usually beats rainbow aggro and life aggro. Sometimes will get rushed down too quickly though.
Special note: parallel universe can be a huge pain. Be careful.