Class doesn’t matter very much in this game, but for reference, here’s their skills:
Black Mirror: (0/25), 1% chance to negate enemy spells per level.
Necromancy: (0/25), 1% chance to ressurect allied creatures that die as a random Death creature with 50% health.
Pact of the Damned: Your creatures split 1% of the damage taken from incoming attacks per rank.
Plaguebearer: Gives you a 2% chance per rank to inflict Infection or Disease on all enemies at the beginning of an encounter.
Unholy Consumption: Each rank increases your chance to find pills whenever you acquire regular items.
Now, if you’re below level 40-50, I’d just go ahead and start a new game in a seperate file rather than spend Emblems on a Robe set, because it won’t take you long at all to catch back up, and before then you really should only be spending Royalty on investments; more Duty rewards, better Power spells, more spellbook/ritual slots, etcetera. Once you’re comfortably set there and ready to start making a combat mage, dump points into Plaguebearer, as it’ll hamstring an entire enemy team for you any time it goes off. Necromancy is also a decent investment - free creatures are always nice. Unholy Consumption is very much an endgame powergaming gimmick and you shouldn’t even worry about it, because even with that maxed out you’ll be in triple-digit floors before you see any pills, most likely.
If you want to be ‘in theme’, here’s a general team for you that’s available early on, within the first six or so tiers:
Raven Acolyte (Sorcery): Causes all creatures in a battle to begin at half health. Turns Disease into a lethal tool and gives the next creature a massive boost. Doesn’t have the stats for tanking or dealing damage, so give it an artifact with a ton of status-inflicting enchantments and use it to disable second-tier threats.
Fallen Carnage (Death): This thing gets ugly as soon as it kills an enemy; it gets a 50% heal, gains Multistrike, and a free turn anytime it knocks something off. Give it an attack-boosting artifact and have it kill things. Put it in the top-left slot so the next creature buffs it with its first hit every time.
Blood Hound (Death): Decently damaging and quick, and buffs the Carnage’s damage output with Direwolves. Fairly useful.
Horror Hound (Death): Causes Direwolves to have 15% chance to inflict bleed per stack, and also is decently offensive. More power for your Carnage.
Scourge Mummy (Death): Inflicts five turns of Burn on all enemies at the start of the battle. Pretty useless on the attack thanks to a base 25 attack, so use it as a secondary tank or for more status-shotgunning.
Stronghold (Chaos): Tanky perfect-Provoking wall, something like this is necessary for all teams. Make it unkillable, HP/All Defense boosts and so forth.
There’s other builds, obviously; the Omnipotent Deity (deals 15% total HP damage to all enemies on any death), a Wicked Carver (gets a 50% boost in attack and a free turn any time one of your creatures die), and then a pack of self-rezzers, like Gimp Mummies or Royal Phoenixes is a classic. The only issue there is finding the Deity, because it’s not an early game drop at all, and it’s key to the build. But hey, you should have a good idea what to do now.