Deck Helper comment: This deck was posted before the 1.32 game update and as a result may work very differently now. Use at your own risk.
This is my first post, but I thought I'd share a deck I've been using (something very similar to this) to quickly farm away at gold/platinum arena matches. I'll note that some games I just quit -- it either wins quickly or loses quickly.
Similar to Instosis
http://elementscommunity.org/forum/index.php/topic,32309.0.html [nofollow].
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The concept is pretty simple. Draw the combo of Mitosis + Silurian dragon + Sky blitz + Shards of Readiness and use it all on one turn. It may seem like a lot of cards to combo with, but drawing them isn't actually all that unlikely. Here's some math:
1 Silurian Dragon with Mitosis + 8 copies from shards = 9*13 = 117 damage
With Sky Blitz = 234 damage
That's enough to kill most arena decks. I can sometimes get away with 3 shards if nymphs dealt damage earlier or even less if the deck has low hp.
The Golden Nymphs (I only have one, unfortunately) are great with a Shard of Readiness. They draw 2 cards right away and 1 more each turn they can activate. The sundials keep you alive and also draw 1 card each, which gets you closer to your combo goal. I'd like to try the Shard of Bravery, but the trainer doesn't seem to have it right now.
Multiple black holes can just be too crippling for this deck to handle, so I'll often quit with those.