I am working on an 7DRL entry titled PossessorRL (not definitive). I am exploring game mechanisms around possessing enemies to acquire their special abilities and overcome challenges produced by the game. I would like the player to not get attached to a particular body and have to change bodies quite often. That should have an impact on the way the game is balanced (no overpowered hero)  and generate interesting choice situations.

For now, I have started the python tcod tutorial to get my hands on the library. I'll be working on evenings only so don't expect anything great ;)

-- edit: changed title to reflect new name

good luck! Seems like a really cool idea

That's nice :D Keep us posted on your mechanics ideas!

Day 2: implemented a controller system to be able to impersonate any monster, and the possess spell which makes use of it. Also added a few story screens when starting a new game.

As for mechanics, I settled for:
- the possess spell only works if you are alone with the monster close to you, for a few turns (monsters will try to stay grouped to avoid that, spells like confuse may help you)
- when you unpossess a monster, it might come for you with a lot of anger
- no healing is possible, so that you have switch bodies often
- one problem I foresee is trying to bring with you multiple utility bodies. To avoid that monsters will have a non-trivial chance of dying when unpossessed
- the inventory stays with an unpossessed body (maybe I will start with no inventory at all)

The trick is to create situations where possession is an interesting mechanic. For example, you have to cross a lava river. A bat is on the other side so I can drop a fruit on the floor to attract and possess it. Or I could use a fire elemental which is immune to lava. However there is none around, so I possess a sorcerer who has the spell for summoning one. Unfortunately he doesn't know the spell, so I bring him to a library and "convince" the librarian to give me the scroll.

This looks like it will be difficult to setup generativelly but I have ideas... 

Day 3 (quick morning update): woke up early and changed AI so that monsters can target any other monster. Added factions so that monsters from the same faction do not attack you unless you start a fight. 

Day 3 (evening): Added lava rivers which hurt! unless you are a fire elemental. Played with tcod noise generation without success, so the rivers follow a simple snake which randomly turns a bit left or right.  It's nice but easy for the player to get stuck. Making sure the exit is on the same side of the river as the player could be an option.

I will try to implement 5 or 6 challenges like the lava river and pick one per level.

Day 4: I implemented a few spells, and monsters to use them. I added a tutorial and fixed quite a few bugs. Most elements are in place. In addition to the ending, what remains is balancing and making the whole thing fun ;)

Day 5: Spent a lot of time implementing a system for monsters to perform actions (incl. casting spells), with associated AI. Added an ending. I ended up dropping item/inventory/levelling support as it unnecessarily complicates the game.

One unintended consequence of the possession mechanism in the absence of levelling is that all critters should have about the same stats, otherwise the player gets killed very quickly. If a monster is overpowered, you have to make sure a counter-monster is present in the level to bring back balance. This makes it very easy to create frustrating experiences. So it may be a mechanism more suitable for short games.

What do you guys think about it?