The combat of the alternate existence game will be inspired by a combination of Frozen Synapse, Divinity: Original sin 2 and Dwarf fortress.
One of the major problems in many turn based combat systems is a massive waiting time for your next turn, bringing combat to a crawl as the number of characters participating increases. This problem is exacerbated during roleplaying, where each action needs to be written out.
To attempt to solve this problem, we need a system that allows everyone to prepare their actions at the same time and Frozen Synapse offers an interesting solution. If we separate turns into a planning phase and an action phase, this means everyone can have time to prepare their actions at the same time and have mere seconds to wait until their next turn.
To further enhance this, it will be possible to write quick macros to use in combat to be automatically used for certain skill actions. The trade off of this will mean that a certain portion of combat descriptions will be automated, much like dwarf fortress handles its descriptions during combat.
A weakness of many roleplaying systems is the way that injuries and damage is calculated needs to be as simple as possible to keep the game flowing, the issue of this is in the unsatisfying roleplaying that comes from these abstractions. Bandaging a bleeding injury or setting a broken bone is much more interesting than healing someone for a certain number of health points. Beyond that it undermines the tension of combat entirely.
Dwarf fortress is built in an interesting way that provides a solution to this everything that exists is built of a material with various physical properties, when one is stabbed by an iron dagger, the game calculates the penetration of that dagger through various layers of cloth, armour, skin and fat, possibly severing arteries and nerves, swung hard enough it could break or chip bone, organs can be punctured or crushed. Imagine playing as a doctor or healer of some kind with such a system. Imagine how on edge someone drawing a dagger in a bar could be.
Combat should not be a frivolous thing that well balanced characters should ever wish to engage in, its a thing of horror and risk, the calculations we will be using will be based on real physics and anatomy. If having your throat slit is all it takes for your character to die, then how do we have a functional community at all? This is one of the reasons of having a verification process, combat should be a dreaded occurrence.
There is another aspect of dwarf fortress that is important, it is not just weapons and armour following physical laws, the entire world is starting from geological layers up to grass being ignited by fire imps. This should remind you of Divinity: Original sin in how it handles such things, though this will be much more complicated as anything could be made out of almost any material. Many wont even notice this, but you may find those who can manipulate the environment to their gain.
A simple example would be the fireball. In most games this would just be a skill that you can use, but in this case it takes a number of skills and many aspects could be negated entirely based on the current situation. The traditional spell could be produced by combining a skill for converting mana into fire, Another for collecting it into a ball and another for projecting it to your opponent. Or your could start a forest fire, and use the fire generated from that as the source for the fire of your spell instead.