In games, RPGs in particular, it's hard to give a good reason to fight/farm a particular enemy or area of enemies. Puzzle & Dragons does a good job of giving reasons to farm particular dungeon, as bonuses of x1.5 drop or enemies that drop particular evolution material. But in a game like FF7, there is very little reason to fight one enemy over another outside of the amount of exp it gives.

I have an action rpg for mobile where players can choose to explore different dungeons, unlocking harder ones as they complete easier ones. My game only has class experience and a single currency, which is in turn used to purchase more classes or more abilities for a class, as player incentives/rewards. So now I am struggling to find a reason for the players to return to a particular dungeon outside of the chance that they are leveling up a weaker class and need to start at the lower dungeons again.

In a game with two small player incentives, what can I do to incentivise players to return to previous dungeons? Should I introduce farm mechanics like "to unlock a class you need currency and this shopping list of enemy parts/items"? What games have you played that you remember giving great incentives to return to previous enemies/dungeons?

Diablo 2, during the end game-phase, gave an incentive to go back to a specific dungeon to farm because of the resistance to certain element, but made sure that all the dungeons gave similar item drops (in your case, it can be xp and currency).

I would say as long as the difficulty/reward difference is negligible, people would farm in their own preferred dungeon for that class.

Should I introduce farm mechanics like "to unlock a class you need currency and this shopping list of enemy parts/items"?

I personally don't like this sort of mechanics, and it's a main reason why I shy away from most MMORPGs that require a list of X items for Y rewards. It forces me to do something that I don't enjoy so I can do something that I want to. Instead, if you can make them want to go back, not just for the reward, but for the enjoyment of playing in that dungeon and then give them a reward on top of that, it's a good system.

thanks for the input, glad to hear I'm not the only one who hates shopping list

Can you scale the difficulty and rewards to the area? For example, Slimes get replaced with Super Slimes that are twice as tough and give twice as much in rewards? (Simple palette swap, slight scale change, or anything else that requires minimum amount of work)

What if you introduce a class ability to get bonuses vs a specific type or group of monsters, and each one you kill provides an incremental component of that bonus?

So if I buy the ability "slime slayer" at 4th level, from that point on each slime I defeat bumps the bonus a little towards the next increment. it would benefit me to go back to the slime dungeon so when I go fight the epic slime boss later it'll be easier.

It would be up to you if there's a limit to how many "slayer" abilities I can train, or if I have to retrain each time I switch it.

This gave me some inspiration. I like the ideas of unlocking skills based on kill counts. Thx

Can you scale the difficulty and rewards to the area? For example, Slimes get replaced with Super Slimes that are twice as tough and give twice as much in rewards? (Simple palette swap, slight scale change, or anything else that requires minimum amount of work)

I'm not the biggest fan of dynamic difficulty but this could work in some situations.