Butterfly effect and steal are pretty much dead cards here IMO.
Steal less so because you might be able to steal a weapon, but still.
Your primary damage will be from casting antimatter and liquid shadow on opposing creatures, so PC is unnecessary.
I would maybe run this deck with some entropy pillars and fewer pends or else toss some black dragons in to balance the entropy and darkness quanta usage.
That said, in general I suggest not buying cards just for Arena decks at your stage because you're going to lose tons of money that way.
The return on your investment is just not worth it.