Would be there lesbian or bestiality or pregnancy?
Like for example:
1- Making a specific number of how many of monsters are in the caves if we said that the total number of the monsters in the game are 100 then for each monster the MC defeat/kill there numbers decrease which makes the game become a bit easier and less combat encounters, and if the number reaches 0 then the MC caused an entire race of undiscovered monsters to go extinct.
2- Adding a pregnancy mechanism with a random chance of getting pregnant (like 20%) and for each time the MC gets pregnant and gives birth to a monster, then the the number of monsters increases, also adding a captured girl in a room that the monsters are breeding with her to increase their numbers, which is making the numbers of monsters automatically increases over time by 1, so the MC need to find the girl and save her to disable the automatic increasing feature (or just ignore her and get out of the caves)
3- adding a stray dog that accidentally got into the caves and got lost for several days now and it's starving, now the MC can choose to feed him if she have some food in the inventory or just ignore it and go on, if the MC chooses to feed the dog it will become her companion and help her in the fight and increase the chances of finding items.
4- adding a safe/resting room for the MC to rest and regain some health, improve her relationships with the girl by chatting with her and with the dog by feeding him, and for the players to save their progress etc.
A- now if the MC save the girl she will stay in the safe/resting room and keep maintaining it which will improve the quality of the room (more health regain, getting 1 food, 1 item, etc) and better relationship with the girl the more health regain increase and better/more food and items the MC gets from her, and when the relationship between the MC and the girl is very high they can have lesbian sex together.
B- for the dog each time you feed him (if the MC had food) in the safe/resting room his status randomly increase by 1, like gets 1 point for either attack, defense, +5 HP or speed (to make the dog attack first in combat) etc, and her relationship with the dog increase and if it becomes very high she can have some fun with him and if she gets pregnant with the dog's puppy and gave birth, she will have a spare dog to take with her as her companion in case of the stray dog died, so if the dog defeated in combat before the MC and the MC lost the battle the dog would die while she get raped, so she need to have sex with the dog and gave birth in case of this situation, so that she won't be forced to fight the rest of the combats alone.
5 - if you have the ability/knowledge to make the game caves/map a random like generator then do it, to give the players a little bit unique gameplays. Like changing the map size/layout, random events, different numbers of monsters/difficulty, changing the location of the girl/dog and the safe room, etc
6- adding a multiple ending to the game like:
A- Ending if the MC got out of the caves alone
B- getting out with the girl (if MC saved her from the breeding rom)
C- getting out With the dog (if it's still alive)
D- getting out with both the girl and the dog
E- ending in case the MC killed all the monsters in the game.
F- an extra/hidden ending, in case if the MC gets out of the caves with the girl and the dog, while her relationship with both of them are very high, then the players will get a scene of the MC having a threesome-bestiality with the girl and dog after they return to her apartment
And good luck with your game dev, and I'm sorry for my bad English.