I made a decent chunk of the interior of my Forest Ruins area, and added in the second "gimmick" enemies of my quest. You see, there aren't going to be any ammo shops at all (plot reasons), but the player's expected to still use items such as Arrows or Bombs. To get around this issue and prevent any tedious ammo grinding, I have specific enemies that are guaranteed to drop ammo refills. For example, when you're low on Arrows, you can backtrack to the forest and look for Forest Archers. Each one you kill is guaranteed to drop Arrow refill items, and they always return to the screen so you can re-kill them all and fully stock up.
Now, inside the Forest Ruins are little pumpkin-headed enemies that breath fire. If you can kill one, you'll receive the Candle! No, this Candle doesn't behave like normal. For that, you'd want to seek out either the Blue or Red Lanterns. While the Red Lantern can be used as often as you want, and the Blue Lantern will only work once per screen, the Candle will work ONCE. That's right, if you use it even once, it's gone for good and you'll need to return to the Forest Ruins and kill some more pumpkin baddies to get another one. Of course, if you use your single-shot light carefully, you might find another stash of enemies in a more convenient location, and make it a bit easier to do some general exploring, but you're going to be SO relieved when you actually find the Blue Lantern and can afford to not be so stingy with your light. This way, the player will have to think carefully about their actions.
Other than that, I've mainly been adding in needed tiles to my tileset, and watching various Let's Plays for ideas on what I can do design-wise. I just finished watching ones on Neutopia and Neutopia II, and am now watching one on 3D Dot Game Heroes, or whatever it's called. Because of this, I'm considering a boss fight in a crowded room with blocks that stab swords out if you get too close. Sound fun?
You should do candle bags, like bomb bags and wallets, so you can carry more than just one.. 
Seriously, though. I've been working out a cheat-code system using the quest name, doing everything from multiple difficulty levels, developer commentary, and other neat stuff. It should be only a couple lines of code, really. One line that sets a variable if a specific name is put in, and then individual lines that do things like weaken upgrades if the variable is set. For instance, if the variable "HardMode" is set, then ammo upgrades increase by two instead of three, and the level caps are made lower. If the variable "CriticalMode" is set, then ammo upgrades increase by only one, and the leveling system is rendered completely non-functional. (Think Kingdom Hearts-style Level 1-Critical Mode challenge) Now that I understand the rudimentary basics on scripting, I've been realizing that things like this are much simpler than they sound.
