Thinking about a typical RPG, but that death is both inevitable and required. Kinda thinking of FF2 on SNES (with Cecil) where you think you're done, but then there's a whole under world. Well, much of the time the NPCs are over-leveled for the players. When PC dies, goes to spirit world type place (like link to the past). In order to resuscitate, player must either succeed someway in the dead world, or arrive at an uplink type spot to get pulled through by players in the light world. Certain powers or abilities are learned while spending time in either light or dark realms. Spending too much time in either affects the story design (e.g. corruption by staying in the dead world for too long)
When PC dies, goes to spirit world type place (like link to the past). In order to resuscitate, player must either succeed someway in the world, or arrive at an uplink type spot to get pulled through by players in the light world could pull through
or a boss of the temple in the dark world, may require multiple dead players to overcome
Can't "mirror" out of dark world… have to fight through. But it's a "mirror image" just like link to the past
secondary skill path.. Unlockable skills only in dark side, but then can maybe at certain brink points link their light level with dark level. Player could have a character who has been "trapped" in the dark for a long time come back
Final bosses, one light one dark, may require splitting team in half to achieve "best ending" = kill both bosses at a party disadvantage (2vB). Otherwise, could group up to take on one boss and then the other… resulting in different endings (only killed the light boss = easiest?)
what about post-game… ruptured world? Where dark creatures spill over? Things like this
Postgame adds a "parallel world" of sorts, regardless of ending chosen. In this parallel world, the monsters are far tougher, there is an ultimate optional final boss, and there is no dark world, so death reverts your save to your last (save points are the temple in the parallel world, which are sparse and require you to really think about your actions.). There are however, much better equipment options available, maybe sidequests, so doing this postgame could result in far better options. Newgame+ is also available upon postgame completion.
Magic elements. Magic points affects your ability to defend / tank. Higher points means less damage. Run out of defense, die faster
"health" in the dark world affects your damage output. Eventually may get "stuck" not being able to fight out alone. Requires bringing "Fresh" characters from the light world to the dark to bail out.
Temples in the dark world are like cracks in the barrier between worlds, allowing light into dark, allowing players to regenerate or escape.
Random encounters? Consider fixed / visible encounters on the light world. Consider random hidden encounters for shadow = scary, lonely, fear
what about time stopping in shadow world. Player can grind in the shadow world, but when they're in the light world they should want to progress the main story.
Magic, specifically shadow magic, is used kind of like Green lantern powers. They can be used to create objects to be used in battle, only manifested through shadow. So they can create temporary giant claws, spears of darkness, levitating swords, or even a spike of sorts. However, there are separate skill barriers, so "shadow magic" encompasses everything, but there are specifically "shadow lance" (deals good damage with a medium critical hit chance) or "shadow swords" (deals multiple heavy damage hits). Each one develops on their own, not "Shadow Magic" as a whole. When a being of light is hit by pure dark magic, they die and enter the dark world/ stay in the dark world.
Dark world shadow "technology" should feel advanced and look advanced by comparison to lightworld stuff.
Light Magic, alternatively, is similar to shooting beams (light array- deals multiple hits of medium light damage, can do anywhere from 5 hits to 13 hits), balls (Heavenly orb- Shoots a ball of light energy that explodes and hits multiple enemies), or something similar to icicle shards (Light pierce- Brings multiple "shards" of light together on a single target, strikes three times for medium damage). Light magic also has specific skill sets that can be bolstered accordingly.
When a dark monster comes into contact with light magic, it explodes into light, creating a very limited healing spot.
Dark is powerful against light, and light is powerful against dark.
More variety comes into play once your two skill sets combine, so you can infuse dark and light magic together for surprising results. Shadow lance combined with light magic can pierce through a light being and burn them, but can no longer deal critical hits. Shadow swords combined with light magic leave cuts with burns that do burn damage, but does less damage than before. Light array combined with dark magic deals heavy damage on all enemies, but can only deal between 4 and 8 hits. Heavenly orb combined with
Concept of using up a lightsource… so if you're in a dungeon in the overworld (light world), where the only interior lighting are torches, then if you use a really BIG light spell, it might extinguish the torch. Minor / major / permanent light sources. Players have MP abilities to reignite light sources. Use the sources to accentuate light magic, or reduce costs, etc.
Reflect mechanics against light-based attacks.
absorb mechanics against dark-based attacks
Aesthetics… light world seems "normal" -- perhaps druidic? Lots of nature, outdoorsy, sunlight. Going into caves should feel like a risk because it's out of the light. Dark sides of large mountains. Naturally obvious to player where it would be "more dangerous" based on how the sunlight hits the terrain. Does not mean that all "bad stuff" in the light world is darkness-based, or exists only in the shadows. There will be "normal" light monsters in plain daylight
dark world is pitch black. Also, more advanced or technological. No real way to see the horizon line. Silhouettes and glinting eyes, dreary illumination from distant cracks in the firmament, light temples, and other landmarkers give players a direction to generally go. Can only see a little in front of them, think diablo2 light radius. Maybe the boss is periodically seen as it walks through the small light sources. Huge. Lumbering (flying?) in the distance, very scary / foreboding. Limbo world aesthetic?? Colors could matter in the dark zone. Player and friendlies are the only colored entities, otherwise everything else is black / grey, some form of shadow or darkness manifest
Characters
Mixture of people from both the light world and the dark world. Some could possibly be spies, based on how evil you are (how many times you kill them in order to gain access to the dark world. The more times you kill them, the more likely they are to become spies.
Post-game, dying in dark world ends up with an entire 3rd layer!!! Reason why you can't revive other people from your world- they were killed in the dark world, and as such, couldn't escape from the third world. However, by killing all the monsters in the light world, and then the dark world, the player has condemned everyone to suffer with the monsters and dark boss and light boss. Postgame requires player to enter third world (knowing that they can never return to their own worlds) and take on the combined light and dark boss- literally something huge and the epitome of light and dark combined. The ending either has the player taking everyone out of this third world, or finding that this new world is much better off, and staying.
Light world back story
Why do we even care?
The best way to get attached to things in games is a desire to protect it, whether it's because the player likes a certain character, or they witness something terrible happening.
Maybe start off slower, build the characters of the townspeople, have something bad happen to one of the most loveable, and when the PC goes to get revenge or something of that nature, have them discover the dark world. And the story can continue on somewhat from there.