I have a player who's playing as a Tortle (DND 5e) and weighs over 500 lbs. This combined with the ability for Tortles to hide in their shell led to some interesting crushing-related activities, and I had to homebrew rules on the fly. Two specific scenarios came up:
From a standing position, the Tortle falls prone onto a smaller creature (eg a goblin). In this case, (the goblin only had like 6 hp) I gave the goblin a dex save against being crushed (instakill) as there's no way any regular goblin could withstand 500 lbs.
From a ledge above a pinned enemy, the Tortle shelled up as it tipped over the edge and fell 30ft on top of the enemy. Again, I gave the enemy a dex save but this time I used the fall damage 3d6 as damage dealt and had the Tortle take half damage because they're shelled up and not impacting a hard surface directly.
Are there any rules for crush damage? Proven homebrew alternatives?
Are there rules for reducing fall damage by landing on someone else? Can the fall damage be transfered?