Udonkronus
Greenhorn
I'm suggesting a procedurally generated (random every time the player enters) dungeon which resembles something like those in the Legend Of Zelda with simple "push the boxes/boulders", "light the torches" kinds of puzzles, some traps, and a small (something tolerable for mobile players) amount of bullet hell.
To go a bit further in depth:
Each floor is multiple square rooms depending on map size, the exit is always accessible and rooms don't lock on the player if enemies are present.
Puzzles can be failed and won't reset.
Moderate amount of monsters per room which shoot projectiles.
Traps which are hidden but have slight giveaways (bombs, pressure plate and arrows, etc).
Loot: no idea, I would imagine not all players are looking for this kind of experience so whatever can be found will have an alternative source. It's just this dungeon will provide those items in more abundance.
To go a bit further in depth:
Each floor is multiple square rooms depending on map size, the exit is always accessible and rooms don't lock on the player if enemies are present.
Puzzles can be failed and won't reset.
Moderate amount of monsters per room which shoot projectiles.
Traps which are hidden but have slight giveaways (bombs, pressure plate and arrows, etc).
Loot: no idea, I would imagine not all players are looking for this kind of experience so whatever can be found will have an alternative source. It's just this dungeon will provide those items in more abundance.