Well, here it goes. Npcs could offer new services, or even other kinds of goods depending on the furnitures that are in their room. For example, the Merchant could offer to you a wider range of goods if you place a chest on his house. If you want to expand the idea, beside that will be a little more tricky, the npcs could offer certain items for sale depending on the items stored on... Storage furnitures (like chests) inside the bounds of It's house, being that the thing offered for sale may not even be craftable by the player, but the npc can offer it to you. Of course, buying that item means that the resource will be depleted from the chest, possibly the player should be aware of what kind of supplies are going to be depleted when buying that item. The nurse, she could even sell you buffs if you build an Alchemy Station on her house, beside that could possibly devalue potions if badly implemented... The moon phases doesn't offer much diversity on the world, most likelly they influence either on the spawn rate of Demon Eyes (or the Werewolves spawn), or a lot of shops items for sale. But what if certain enemies only starts to appear during certain moon phases? That could be a rare thing for the player to find during it's travels, or the most dangerous thing ever. Of course, those spawns should offer something to compensate the player. The player also could be able to find friendly npcs during their travels, like a certain raccoon peddler that shows up on 4/8 moons at the surface, any time of the day, during travels... Underworld mobs having loot. (I wont quit asking for that) I'm not necessarily asking for weapons or equipment drops, like used to be serveral updates ago, but they could drop materials for crafting extra gears so the player get ready for the challenges. I'm talking more specifically about pre hardmode underworld, by the way. The spider biome would be more deadly, and even farmable, if they could sometimes spawn cobwebs around the place they are, like a circle of cobweb. That would turn fighting against them more hardcore, aswell better to farm cobwebs when the spider biome is empty of cobwebs. Or even spawn cobwebs around the player when the player is near the spider, turning it harder for the player to escape. Of course, for that to work, there should be walls where the player is at. Talking about the spider biome, the Creepers could offer some loot on pre hardmode, something useful that the players could find from them, or even use to craft something, so they are less of an obstacle, and more of... Well, you think about the word. Some biomes could have night version of their music, like the Corruption, Crimson, Tundra and the Jungle. The night version could add to the climax of the biome, and also allow the player to know when It's day or night, without having to check the clock. Of course, the night music would only be listenable at the surface. Also talking about night version, to not make the players life easy, nights could be more dangerous on a range of biomes, let's say the corruption and the crimson, there could be new types of monsters that appears, who are challenging to face, they pump up the difficulty, and makes the night travelling of those biomes more dangerous than the day. Of course they shouldn't turn the night exploration of such biomes a forbidden thing, but not recommended until you are ready to face troubles. The fact that Jungle Bats spawns during the day is really weird, their spawn could be changed to the night, and place another creature to spawn on it's place during the day. Those are my suggestions. Enjoy.