I'm going to preface this by saying that I have no idea if this is important or even interesting to anyone but me, but here we go. I've looked for concrete rules on monster spawning, ways to build a monster spawn chamber/tunnel system/etc. in vanilla, and related topics re: monster spawning in Starbound, but I have yet to find a concise answer on any of those. So I decided to do what I do best: screw around with it and report the results. I should also mention I am using the RPG Growth mod (Steam Workshop version) and that was my primary reason for conducting this experiment. I don't believe RPG Growth or any of my other mods affect monster spawn rate or locations, and none of my mods add monsters to the wild that I know of, so this should still be relevant to vanilla players. Obviously, if you use FU or other mods that change up your spawns, this could be really different for you. SETUP I chose a Forest (tier 2) planet orbiting a Gentle (tiers 1-2) star with a Giant Flower biome for my location, as I intended to hunt Mandraflora. I used tier 5 Aegisalt armor, an Aegisalt pistol, and a (tier 4?) shield. BUILD Since my biome was pretty small, I decided I'd have to use caves as well as the surface to maximize my spawns. I opened up some natural cave formations (and blocked off some others that were too small or went too far out of my way) and connected a few of them together, and lit them all up. I did not add or remove any background tiles while doing this. (I've heard that player-placed background tiles can prevent spawns.) Some of my cave areas were too small to spawn Mandraflora, so I widened them. On the surface, I removed dirt blocks or added wooden platforms so that I could run from one end of the biome to the other uninterrupted, without ever jumping or breaking my sprint. The left edge of my biome at 1x zoom. My caves went pretty far down. Placement of torches and platforms was key. Close to the right edge of the biome. I'm mostly showing off how effective it was at spawning Mandrafloras. These guys were all just hanging out here when I came to take screenshots. PROCESS When actually hunting the Mandraflora, I started on the left edge of my biome and ran across the surface, killing anything I found along the way and checking the caves I could see for spawns. (If I saw a Mandraflora I'd jump down to kill it, but I left Bulbops alone at this stage.) Then, when I reached the right edge of the biome and the cave entrance there, I jumped down into the cave and cleared it of any spawns. Going back from right to left across the biome, I went through each and every cave to make sure I cleared them of everything I couldn't see from the surface. Then, when I reached the left edge of the biome, I ran back across the surface again. THINGS I NOTICED Light had absolutely no effect on spawn rates. Monsters spawned in the dark just as much as in the light. Due to this I ended up lighting up most of my spawn area so that I could more easily see anything that spawned. I never once saw anything spawn on-screen. I'm not sure if this is affected by zoom level, or if there's an area around the player in which nothing will spawn, but my assumption is that you'll get more spawns if you keep moving, so the areas you leave behind can spawn. There were two natural pond formations in my biome, one much larger than the other. I ended up draining them both of water and monitoring them for spawns, but I found no evidence that either one spawned any monsters, even once drained of water. I put a layer of dirt over the original area of the small pond, and completely filled the large one with dirt. I still found no evidence that the small pond was spawning monsters, even after adding dirt, but I did find a few monsters inside the area of the large pond once it was filled in. That doesn't necessarily mean they spawned there, however, as they could've spawned outside the area and walked in. In future builds I'm going to completely ignore ponds like this, since it doesn't seem worth it to totally fill them in for a chance they might spawn something. The smaller pond, near the right edge of my biome. The clay is its original bottom; I added the dirt on top to see if that would affect spawning. It didn't seem to, so I ended up just letting it fill back up with rain. This is where the larger pond used to be. I totally sealed it up with dirt to see if that would affect its spawning capabilities. Still not sure whether it did or not. RESULTS In roughly 1 hour, I went from about 10 spiral energy to 37 spiral energy. I also got 61 living roots and 5 leather (from generated monsters on the edges of the biome). I gained 2 levels during the process (from 28 to 30) and another on my way back to the biome to take screenshots (leaving me at 31). I also got roughly 5,000 pixels. I found 1 Poison Mandraflora and 1 Poison Bulbop during the process (which I captured), and one more Poison Bulbop when I went back for screenshots. My bounty. (Stored in Capture Pod Cupboard from the Enhanced Storage mod.) Reach within your local cave and you may find a friend and boy. POTENTIAL USES FOR AN OPTIMIZED SPAWNING BIOME For me, I made this mostly to see what affected monster spawn rates, and to gather spiral energy and experience for the RPG Growth mod. However, even in vanilla Starbound I could see this being a useful technique to gather large amounts of resources relatively quickly (like the living roots - if you choose a planet/biome that can spawn Smoglin, for instance, you could get many scorched cores, or meat and leather from generated monsters if you're using a bow...). In addition, it could be used to farm pixels, specific action figures, or find rare variants of unique monsters (like the poison Bulbop and Mandraflora). STEPS TO MAKING A MONSTER-SPAWNING BIOME Based on my result, here's how I'd go about setting up a biome for maximum monster spawns in the future. Step One: Choose a Star and Planet/Biome Consider what monster you're looking for, what tier(s) of planets you'd like, and if you need a specific biome/planet type for your hunted monster to spawn. More Planet Info is a useful mod for finding specific biomes. I wanted to find Mandraflora that I could kill easily. Mandraflora spawn in Giant Flower biomes. Since I wanted them to be low-tier, I went to a nearby Gentle Star and searched the planets there. I found a Forest planet with a Giant Flower biome, which I used for this project. Step Two: The Surface For this step it's helpful to have a stack or two of some form of building block (I used dirt), and maybe 50-100 of some kind of platform (I used wood). You might need more or less than this if your biome is bigger or smaller. Start by figuring out roughly the boundaries of your biome. You can mark these if you want. I had a cave entrance at each end. Next, you'll want the surface area of your biome to be easily traversible on foot. One way to do this would be to add or remove dirt blocks to totally flatten it, but that could take some time. I simply removed a few dirt blocks and added some wooden platforms to make everything no more than a 1-block incline, and covered any drops, ponds, and cave entrances with platforms. Since it doesn't seem like monsters can spawn in ponds (even if they've been cleared out or filled in), I would recommend just putting platforms over any ponds you have and otherwise leaving them alone. Step Three: The Subsurface I relied heavily on my Cave Detector during this part, both to find caves and to make sure ones I didn't want were filled in. Drills or pickaxes can also be helpful, as well as the building materials from the previous step, and torches. If you can see or have already stumbled upon some natural caves near the surface, either make yourself a path to them or just jump down into them now. Decide how far down you want to go. (At some point Starbound will limit this for you, since the biome will change the further you go down. If you don't need a specific biome, though, and you don't mind the one you find underneath, feel free to go as far as you want.) Optionally, you can fill in any natural passages that branch off outside your biome, or go too far down/out of your way. This can take some time to do, but will prevent monsters spawning in those areas that you can't get to and clear out. (I'm not sure if there's a limit to how many monsters can spawn in an area at a time, so I don't know how much this will affect.) I filled in a few meandering passages here and there that would take more time to check than I wanted to spend, but I left the edges of my biome mostly untouched. If you plan to spend a lot of time here, you may want to make sure your biome is pretty well boxed in. Consider how big the monster you're hunting is - and how big any other monsters that can spawn in the area are. Mandrafloras are fairly large, and the only other thing that can spawn in a Giant Flower biome is Bulbops, so I carved out all my caves so they were big enough to spawn Mandrafloras. If you're hunting something smaller in a biome that can spawn larger creatures (Gleaps, for example, are typically in areas that can also spawn large procedurally generated monsters), you may want to keep your caves relatively small. Finally, connect your caves as much as you'd like. I started with maybe 7 or 8 caves and ended up with 4 mid-size connected cave systems throughout my biome. You can totally connect them if you want, but most of my caves naturally returned to the surface anyway, so I just hopped out there and jumped down into the next one. Optionally, you can light up your caves, especially the ones near the surface. The light doesn't affect monsters spawning as far as I could tell, but it made it far easier for me to see them. As such, I could potentially skip a small cave if I saw that it had nothing in it, which saved time. Step Four: The Hunt Is On! For this step, you will obviously need your weapon(s). It can be helpful to bring food, healing items/a tent, a shield, and a campfire (to cook meat that drops). I was using the Sprint tech, which made it a lot easier to get across the surface of my biome quickly. Pulse Jump, another jump tech, ropes, grappling hooks, and/or careful placement of platforms can help with getting around your caves. As I explained in my process, I found it best to start at one edge of my biome and run across the surface, then head down into my caves and make my way back across underground. You can do it however you want, but I found it helpful to keep moving. While doing this, if you didn't block off the edges of your biome to trap everything inside, then be sure you check a little past the edges each time in case something wandered outside.