Ok, I'd like to gather some decks here that we might play.
First, there's mono Darkness. It will often rely on the Dagger/Dusk combo to retin the edge in a race. Steal can be used as PC depending on whether we expect it. Drain Life is ok CC here, good vs creatures with up to 4 HP, kinda weak against the rest. Devourers are good if the opponent is not rainbow and not too fast of a rush. Black Nymph can be kept in mind mostly as an expensive Parasite (could be good against stuff like RoL Hope).
Mono Dark NoDev
Hover over cards for details, click for permalink
5uk 5uk 5uk 5uk 5uk 5uk 5uk 5ul 5ul 5ul 5ul 5ul 5ul 5uo 5uo 5us 5us 5us 5us 5us 606 606 606 606 606 606 606 606 7tb 7tb 8pt
Mono Dark Dev
Hover over cards for details, click for permalink
5uk 5uk 5uk 5uk 5uk 5ul 5ul 5ul 5ul 5um 5um 5um 5um 5um 5um 5uo 5up 5up 5us 5us 5us 606 606 606 606 606 7ta 7ta 7tb 7tb 8pt
Devtal - the version below is mostly tuned for fast Devtal combo which is probably best against stalls. The opponent will have the chance to play a few cards before that though, so it is not so great against rushes. That matchup can be improved by taking more defensive cards like Dims, Lightning, Dagger, etc.
Devtal
Hover over cards for details, click for permalink
5um 5um 5um 5um 5um 5um 5ut 5ut 606 606 606 606 606 606 606 606 606 606 606 606 606 606 606 622 622 622 622 622 7ta 7ta 8pu
Darkness Grabbow is ok but not super exciting so I have been thinking about alternative rainbows. This one has a strong focus on denial with Discord, Devs and QS. Similarly to Devtal, the problem is that the opponent can usually sneak in a few threats before we can lock him out. The deck itself is also quite slow and the creatures are somewhat fragile. Reverse Time could be a good addition here.
Discord Massage
Hover over cards for details, click for permalink
4vh 4vh 4vj 4vj 4vj 4vj 4vj 4vj 4vl 4vl 4vl 4vl 5uk 5uk 5um 5um 5um 5um 5um 5um 5up 5up 606 606 77j 77j 7t5 7t5 7t7 7t7 8pj
Here's a stall idea. Pandemonium should have some great synergy with healing cards and Diss Shield.
Panda Stall
Hover over cards for details, click for permalink
4vg 4vg 4vg 4vg 4vp 4vp 4vp 4vp 4vp 5uk 5uk 5uk 5us 5us 5us 5us 5us 606 606 606 606 606 606 606 606 606 606 606 606 606 606 606 7tb 7tb 7tb 8pj
Time-Darkness duos are pretty strong, but actually in my opinion not due to Ghost-Nightmare. It's just too easy to play around it in PvP. When we were playing this deck on team time we won the vast majority of games due to card advantage from random Time Nymphs, Hourglasses, Steals or Eternity, playing more of a stalling game with RT.
Here is a cute idea with Devs that also uses Vamps for healing. A more conventional build with different creatures might be better.
Vamp Rt
Hover over cards for details, click for permalink
5rk 5rk 5rk 5rk 5um 5um 5um 5um 5um 5um 5up 5up 5ut 5ut 5ut 5ut 606 606 606 606 606 606 606 606 7q5 7q5 7ta 7ta 7tb 7tb 8ps
I'm a fan of Nymph's Tears and Steals can help with problematic shields while Dagger gives time to get a nice spam going. It's still kinda slow thouhg. A more stalling build with Squids might be better.
Nympies
Hover over cards for details, click for permalink
5i4 5i4 5i4 5i4 5i4 5ig 5ig 5ig 5ig 5ig 5ig 5jm 5jm 5jm 5jm 5up 5up 606 606 606 606 606 606 606 606 606 606 7t8 7tb 7tb 8pp