***TRIALS RESPONSE***The first thing I noticed about your deck is that it is 60 cards. Very few decks are that big, and virtually all the good ones have ways of drawing through their deck faster. Yours does not. 60 card decks are bad because the chance of drawing cards you need lowers dramatically, making them very unreliable.
The second thing I noticed is that your deck is severely lacking in quanta. With a QI of around 8.3, this deck has severe trouble playing its cards (not to mention powering its Drain Lifes). I would suggest adding a lot more pillars normally, but first we must deal with the size problem. Once we have done this, the amount of quanta usage will inevitably come down.
By reducing the deck size to 30, you're also reducing the number of different unique cards you can have in your deck while keeping it reliable. Unfortunately, this means that your deck will be changed drastically, and that by reducing the size of this one you can get virtually ANY Mono Darkness build.
Because you say this deck is for Arena, though I'd suggest this one, posted by regen2k9 (
http://elementscommunity.org/forum/index.php/topic,30564.msg481739#msg481739) and designed for Bronze League.
Hover over cards for details, click for permalink
5uk 5uk 5uk 5uk 5uk 5ul 5ul 5ul 5ul 5ul 5ul 5um 5um 5um 5um 5um 5um 5up 5up 5up 5up 5ur 5us 5us 5us 606 606 606 606 606 8pt
Why is this better? Firstly, it has 30 cards, making its draws much more reliable. Secondly, it has a much better quanta balance (a QI of about 5.6), allowing it to play its cards much more easily. It is also tested to have an 84% winrate against Bronze League, albeit with a small sample size.
You can take many different paths when improving this deck. Just stick to 30 cards unless you have a good reason not to, and use the QI calculator (
http://elements.alanbeam.net/qi.php) to get an approximate quanta balance for most decks. I hope this helped.