This is my second challenge (here's my first from 2018) but I'm sticking with a 2D top-down view this year.
Sorry I'm only finding this message board now but I have been working on my entry since 2 March.
My idea is to let you explore the dungeon backwards. i.e. You already have the MacGuffin that you were originally questing for and now you are at the bottom of the dungeon and need to make your way up.
This means that I can put all the nest/coolest monsters, items and other mechanics in the "first level" the player interacts with; rather than trying to build up to it; and I think most players (at least, my friends who don't often play rogue-likes) can see what's at the bottom of a dungeon. The end screen shows how much was explored and anything interesting the player might have missed.
As of writing, the player can navigate and escape the 10-level dungeon and get the end screen. There are also hidden tiles and fog-of-war. There is a message log. There is a single, un-acting monster type which the player can damage and kill and healing potions which are automatically picked up but cannot be used.
I'm currently implementing a scheduling system so the monsters can move and attack back.