Very nice ideas, again. You've set the bar pretty high, ScytherLoL - I'm going to be expecting this level of ingenuity and artwork every time you set foot in this part of the forums!
hehe just kiddin'.
But yeah, few things I'd change if it was my idea (or what I think will make this a better addition to Elements.)
Abyssal Apprentice
Cost: 5 Darkness
Stats: 2/4
Ability: 2 Darkness: Summon Ghoul
Abyssal Wizard
Cost: 6 Darkness
Stats: 4/6
Ability: 2 Darkness: Summon Elite Ghoul
Ghoul:
Cost: 2 Darkness
Stats: 2/1
Ability: Absorb Quanta: On each successful attack the Ghoul gains +0/+1 and steals 1 random quanta from your opponent, adding it to your Darkness Quanta.
Elite Ghoul:
Cost: 3 Darkness
Stats: 3/2
Ability: Absorb Quanta: On each successful attack the Elite Ghoul gains +0/+1 and steals 1 random quanta from your opponent, adding it to your Darkness Quanta.
Simply put, these changes balance it a bit more (in my opinion).
1. Less offense, more defense on the summoners - their offense comes from summoning.
2. Reduced cost of summoning Ghouls.
3. Added an ability name for the Ghouls, it can't just be blank!
4. Added an elite ghoul, basically a +1/+1 Ghoul.
An alternative idea I just had while re-thinking this a bit, would be to make the ghouls start off with a high offense and a low-ish defense, such as 3/2 normal, and 5/3 upgraded. When summoned they start off with 1 poison counter on them, so normal attacks 3 times, and the upgraded one attacks 4 times before dying. They gain +1/+0 per turn and steal quanta from your opponent. So a normal ghoul will be 6/0 on it's last attack, and the upgraded will be 9/0 on its final hit.
I think this idea is a bit too similar to Firefly Queen - in that, the only major difference is the Fireflies get stronger each turn and that they steal quanta. I would keep this as a template, but alter it so that it has more synergy with Death cards - Death and Darkness go hand in hand, happily ever after...
... This way, Boneyards and Bonewalls as well as Vultures can also benefit from the Ghouls automatic death.
Just my two cents