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MOD IDEA
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I will preface these ideas by saying that I do not have the ability to program so if someone want to take the ideas and run with be my guest. I have some design and artistic skills I can assist with skins if need be.
Now as for my ideas. I would love it if we could have a mod that would add a tool belt and weapon holster. The tool belt and weapon holster would be items that you'd place in your hot bar that would allow you to hold several tools/weapons in that slot at once. You could then toggle through the tools/ weapons to the one you want to use saving space in your inventory and while having the convenience of your desired tool/ weapon a hot key away.
For example let say the tool belt is in your first slot. If you shift click you can open the interface and add tools to the belt. There can be one two or three tiers of belts that hold more items. I'm thinking the first tier could have 3 slots, the second 6, and the third 9. If you had the level 1 belt you could add the pickaxe, axe and shovel. When you want the particular item you press a hotkey to toggle through the tools. The same functionality would be used for weapon holsters. You could add swords, bow, etc to that. It would really be cool if the belts with the items could be rendered on the character.
Crafting the belts and holster could be done on a sewing machine that has an interface that similar to the crafting table. The recipe could be leather and string. Maybe the leather need to be treated first or put together to form a pattern and then sewn together to add steps to the process for the upper tier versions. The belts/holsters should be able to be dyed for customization.
The machine for this mod could be a sewing machine like I mentioned previously. The low tier sewing machine could be manual simulating using a foot pedal that consumes hunger bar. The 2nd tier would of course use power of some sort (BC perhaps). Another machine could be a loom to make cloth from string or cotton or other existing modded plants. You could use these machine to make other items like curtains rugs and carpets that can be upgraded or enchanted perhaps to enable or prevent mobs spawning, or teleportation etc... You could make a shoe making machine to make shoe and boots with different bonuses or abilities. For instance if you craft leather, rubber, string and those pesky quartz from Xycraft you can make boots with climbing spikes that allow you to climb up/down anything like ladders.
With machines like that you of course are going to need a variety textiles. We should kill a few birds with one stone and add alligators to river and swamp biomes to bring some much needed aquatic life to the game. I envision that they would lurk in water near shores waiting to snatch unsuspecting prey. If they happen to snatch you then expect to be dragged into water to the bottom to be drowned unless you can fight free of their grip. Maybe some sort of boots can be crafted that will help you protect yourself from these encounters. Of course if you are able to kill the alligator you should be able to fashion a host of items from their skin. "Now or Later Gators" anyone? Or how about snake skin items from the hides of pythons from jungle biomes or sidewinders in desert biomes or the deadly black mambas from savannah biome or water moccasins in rivers and swamps. Plus with the introduction of venomous snakes there's an opportunity for creating potions/antidotes that can then be crafted into poison arrows and the like.
Finally I'd love to see some sort of powerful rare air creature. I'm thinking maybe a Gryphon? It could attack players and villagers out of the blue by swooping down and abducting them. Maybe taking them back to their nest/lair where a great treasure is guarded by them. They could only come out to attack at specific times or conditions for instance, full moons or high flux levels. If you kill the Gryphon then some special item or treasure could yours for the taking.