Dark

skill

Darkness

1

D+

Channel 1 Dark.

skill

Dualcast

1

B-

Evoke your next Orb 2 times.

skill

Multi-Cast

X

B

Evoke your next Orb X times.

skill

Recursion

1

C-

Evoke your next Orb.
Channel the Orb that was just Evoked.

Dark orbs can be trickier to use than frost or lightning orbs but scale very well.

Certain cards allow you to benefit from the stored up power multiple times. Dualcast is a synergistic card from your starting deck, and Multi-Cast can triple an orb's damage (or better)! Recursion can generally be quite an unimpressive card, but when used on a Dark orb it maintains all of its stacks, allow you to deal damage and continue scaling.

Darkness is a cheap and simple source of Dark orbs and typically sufficient. I would recommend upgrading defensive options before upgrading Darkness since the additional effect comes in handy more rarely.

attack

Doom and Gloom

2

C

Deal 10 damage to ALL enemies.
Channel 1 Dark.

attack

Bullseye

1

C-

Deal 8 damage.
Apply 2 Lock-On.

power

Defragment

1

B+

Gain 1 Focus.

power

Loop

1

B-

At the start of your turn, use the passive ability of your next Orb.

skill

Coolheaded

1

A-

Channel 1 Frost.
Draw 1 card.

Symbiotic Virus

uncommon

At the start of each combat, Channel 1 Dark.

B-

Any source of dark is fine: Doom and Gloom can be nice early on as it helps to clear low HP trash enemies like Gremlin summons without your Dark orb targeting them; Symbiotic Virus can't be relied upon but is a welcome adition to the build.

Focus and Orb Slots, as always, can be useful, especially if relying on Frost orbs as a means of defence in this build, but they are less important than usual. Loop, however, is very powerful, since it doubles the potency of your first slot, and you would prefer all of your damage bundled into one orb because of Dualcast and Multi-Cast.

For this same reason, don't feel obliged to pick up every dark orb source you see - one is enough, two is plenty.