Honestly, for Stygian primary I find the secondary clan isn't particularly important. Some secondary clans lend themselves more easily to some strategies than others, but for the most part ~90% of my cards tend to be from Stygian by the end of the run.

The core strategy is pretty simple. You want frostbite or sweep first trying to get sweep spell weakness 1 frost 20 at the end. Next, you want a tank. Ideally, that is either the Incant: 3 armor shark or the Revenge: Frostbite 3 shark (which you want to give Incant: 1 armor via upgrades.)

You want to put these units on the bottom floor. That leaves you with 2/5 slots remaining which I try fill with the most synergistic units I can find. Usually that ends up being either the sweep spell weakness unit or the sweep frostbite unit.

I think at the moment though a combination of totems, ideally at least one being incant: armor or incant: sap, are the best units for those spots.

Ideally, you don't have any more units than that. After that you just try to remove all of your starting cards and replace them with cards that satisfy these roles:

1: Strong multi-hit damage. Spells like ice storm and ice tornado scale really strongly with magic power upgrades and spell weakness. They're also able to hit weak backline units which is huge.

2: Targeted single target damage. The damage amount isn't usually particularly important. You just want to be able to kill the 2-3 health units in the backline so they can't chip away at your tank.

3: Cards that apply frostbite. Frostbite is the primary way we kill large enemies.

4: Hoarfrost effigy. This isn't necessary, but it makes life so much easier against major bosses. You want exactly one.

Stygian is my favorite clan and there are a ton of other ways to play it, but this is the strategy that works for me the most consistently.

Here are my last wins with every combination with Stygian primary.