Homebrewing Kick: Lesser Death Knights and Ancient Mechs

My homebrew setting has a couple elements that maybe don't set it apart in terms of their presence, but in their prominence.

It is a setting with a fallen, technologically advanced civilization. It's also one in which there is basically a massive undead army that is currently leaderless and confined to a place in the center of its largest empire with a low population. It also has a great deal of aberrations, with a strong cosmic horror element (that might just have something to do with the fall of that ancient civilization.)

I've brewed up a couple of stats for the final dungeon of the adventure my players are currently on, but I've also been working on a few other elements.

First off, with the undead hordes and elite skeletons, I also wanted to brew up a Death Knight I can throw at a tier two party. Conceptually, what I came up with were "Scourge Knights," named obviously in reference to Warcraft's undead Scourge. Given how the Death Knight is based on the idea of a paladin of great renown breaking their oath, I wanted to make a distinction for these lesser versions. Thus, my lore is that when a Death Knight slays a paladin, they can sometimes capture the soul of that paladin (involving a magical item called a Soul Lantern.) The Death Knight then tortures the soul until they agree to serve the Death Knight, at which point the soul is released to manifest as a corrupted, undead lieutenant.

Splitting some of the Death Knight's abilities and coming up with some new ones, the first of the two varieties here is Scourge Knight Captains - which can lead contingents of undead and retain the Death Knight's more defensive capabilities. The other is Scourge Knight Executioners, who wield greataxes and have a feature that makes it far easier for them to get to their foes.

The Captain and Executioner are CR 10 and 9, respectively, allowing you to throw them at a party far earlier than the CR 17 Death Knight.

The really big project, however, has been my Ancient Mechs. These are basically robots that patrol the post-apocalyptic wastelands that were never rebuilt following the fall of that ancient civilization. These mechs fight mutants and aberrations, but sometimes mistake the "Scrappers" who try to salvage the lost technology for their targets.

There are several varieties of mech, ranging from the small Scavenger Mechs that are designed to sort through piles of rubble and find useful material (and are the ones I imagine as being cute and probably puppeteered by the Jim Henson company) to the Huge Assault Mechs, which have powerful cannons, a shielding force field that reduces incoming damage, and even a miniature nuclear strike capability.

What unites the design of these creatures is their use of Power Cells. Essentially, each of their main actions requires power from their batteries. And they will continue to operate until they run out of juice. However, given that these power cells involve some magic, they will regenerate on their own over time. Because power cells are interchangeable, other creatures can swap out a power cell if the mech is out of energy, and so NPCs (or even potentially players) who find a way to reprogram these mechs to work for them can keep their mechs working if they have a supply of fresh power cells. Naturally, the bigger ones come with more cells, but they also have abilities that drain more power from them.

Inspired by these mechs, I also started detailing the town of Gonquista - the only major settlement in the post-apocalyptic wasteland part of my setting - giving it a number of factions and important figures heavily (heavily) inspired by Mad Max.