I'm developing a mod (attempting to anyways), and I already have some ideas, like:
• A "TeleBlade", a curved blade which the user can throw. Wherever it lands, the player can then use a keybind to teleport to it whenever they like, at which point they can get it back. They can also throw it and teleport to it while it's still in midair (I actually did that by accident and I loved it so I kept it). After teleporting though, it'll give you a few seconds of nausea. I have had trouble with what it should be made of though, 3 ores (iron ingots, gold ingots, diamonds, etc.) and a stick, but why does it teleport? Should it have an ender pearl on it? Or maybe there's some sort of teleportation book you have to find to make it? Ideas are greatly appreciated.
• "Excalibur", King Arthur's legendary sword. I wanted it to be hidden in a huge tree, like in Terraria, and deep underground, in the roots, is a stone block with the sword in it. Maybe there can be a twenty five percent chance that you can pull it out of the stone or something. It would have to be super powerful, but I always like a drawback, so maybe everytime you kill something you get a negative effect for a short time (or you lose health), or you get a minute of awesome effects, but afterwards you get a minute of bad effects, or it can only be used during the daytime. There has to be something bad so it's not totally OP.
• A piece which sends you to the Nether when you die, with no inventory. To get back you'll have to find a bunch of ghosts and kill them to collect their souls. This would confuse the code of that undying totem thingy, but it's okay, I'll find a way around that. This part would need to add Ghosts as a mob, and some sort of block that can be used to make the portal back using the souls. Maybe using resources from the nether? Also, you would need to be able to make tools for the time that you spend there, so perhaps Quartz tools?