So i've been playing some Warhammer with friends and out of the post revamp shit one thing i actually liked the idea of quite a bit was a mechanic the new Deep Sea Elves use called "The Aethersea".
What happens is these elves that need to raid human coastal towns for souls since their children are stillborn without souls of their own due to slaanesh fuckery use a military force based entirely on tamed/magically bound sea predators, deep sea magic and elves with no eyes and pale skin suited for the sea floor.
To get by they summon an ethersea which makes land behave like deep sea. Blood from wounds bubbles up into clouds, a thick murky air blocks the sunlight like its deep below the ocean surface and as plants and trees behave like seaweed caught in a current barnacles, coral and even ghostly shipwrecks erupt into reality all around these towns now caught at the bottom of a magical sea. The elves then ride in on sharks and eels and giant turtles and shit to steal humans and then when they retreat and the aethersea recedes it takes all memory of the attack with it. Letting them farm the same villages for centuries.
So basically imagine Silent Hills Otherworld transition but instead its deep sea shit. The only game that did this i can think of was a tiny section of Dear Esther where you walk along a english motorway under the sea but fuck i need more.
What shit do you really want to see put in games that never really has been already?