Really cool, actually. I agree Vanguard's ideas make sense.
A problem as it stands, I think, is that it's a bit static. It feels now as if there are situations that become quite deterministic, where the player has little actual choice. Some ideas to consider that might add more strategy:
* Don't allow monsters to skip turn, even if they have no path to player? Make them dance around a bit if the player is hiding behind an impenetrable wall.
* Make healing cost one turn.
* Maybe have several exits from the rooms, and possibly allow monsters to move between them (in some/all cases)? Running away with a trail of monsters might prove deadly, but it would be satisfactory to find a yeti, or to use potions as walls to fend off one horde whilst taking on another.
* Allow (some/all) monsters to use potions? A monster stepping on a red potion could get 1 extra health, for instance. Also: Allow (some/all) monsters to destroy bone walls?
* More monsters of course, but maybe also more terrain types (eg. thorns make you lose one turn when you pass them, destructible obstacles already in place, traps, forest/shadow which make you "invisible" as long as move within them, making monsters stop or wander). In short: More effects to explot (and which the monsters might exploit).
Stray monster thoughts:
* Monsters that grant special movement (move diagonally for N turns, move in one-space jumps for N turns).
* Monster/potion that grants double speed for N turns.
* Monster that eats potions, destroy walls.
* Monster with (seemingly) adverse effect when killed. Killing a jelly makes you lose one turn (which can actually be what you want, sometimes). Multiplying jellies with this effect could prove interesting. Jelly farming would mean a whole new thing (and be extremely dangerous).
* Monster that, when killed, turns the next closest monster (or the next one you bump) into your ally (probably won't be able to leave map).
* "Boss" monsters, which may have special rewards (mana -> 5, raised health limit ...)?
* Giant monster (several tiles big)
* Monster that poisons the ground it has walked on? Other monsters will avoid (treat as wall), player can pass, but it costs 1 health.
Just some loose thoughts. Take what you can use, add salt and pepper. I really like the simplicity of the concept, and think you should stick to it. Adding too many features might take away some charm. But it's still an idea that is really spacious, you can get a really intersting bestiary without adding skill trees, submenus etc.
As always,
Minotauros