Arena decks have to be 35 cards.
So +1 forest spirit +1 nightmare -1 hammer.
The AI is too stupid to play momentum and not the salvagers.
A grabbow in general is not the way to go in this scenario.
Graviton salvager is clearly the arena card.
I would have made this deck, or something similar to it:
Hover over cards for details, click for permalink
55t 55t 55t 55t 55v 55v 560 560 61t 61t 61t 61t 61t 61u 61u 61u 622 622 622 622 63a 63a 63a 63a 63a 63a 63a 63a 63a 63a 74j 74j 74j 74j 74j 8pl
Fractal your salvagers, using gravity pull and black hole and lobo to keep yourself alive, use chimera to fly over your opponent. Can't momentum all of them. If you had Shard of Focus, I would consider using that instead ((If you don't, why am I asking for 3 lobos from you?))
Which brings me up to salvagers not being very useful and that you realistically should just skip it.