I already discarded our deck to make things easier in our spreadsheet.
I don't see any reason not to run an Fractal Dragon Bolt deck against Gravity. Gravity's only decent damage is chargers which fall to Lightning and Fractal Wings breaks Wings, which they will almost surely use.
Gen. MrBlonde vs Gravity
Hover over cards for details, click for permalink
52g 52g 52g 52g 52g 52g 52h 52o 52o 52o 52o 52o 52o 542 542 542 542 542 542 542 61q 61q 61q 61q 61q 61q 622 710 710 710 711 71b 71b 71b 71b 72i 8pu
And here's the actual deck we're going to play.
Hover over cards for details, click for permalink
52g 52g 52g 52g 52h 52o 52o 52o 52o 52o 52o 542 542 542 61q 61q 61q 61q 61q 61q 622 710 710 710 711 71b 71b 71b 71b 72i 8pu
We can't really use anything else here, so I added 6 pillars/pends to the actual deck so we aren't risking more than 30 non-convertible cards.
Darkness is a lot more difficult. Their decks usually have Steals and airborne creatures, which make it hard for us to run Dims or Wings. I think our best shot is a Mono Rush with Bonewalls for stalling. We have 8 creatures in our entire vault, so we have to mix poisons and Bonewalls into both of our decks.