Guardians should have a chance (same as an Ender Pearl I thought) to drop their spikes (Guardian Spike?). This spike could be crafted into a powdered version (Powdered Guardian Spike, Powdered Spike of Guardian?) that is essentially underwater Bonemeal. I thought this underwater Bonemeal could be the only thing able to grow Coral into Coral Blocks, making it a renewable block.
Maybe a spike along with 2 sticks could be crafted into a spear.
The Elder Guardian should have a 100% chance of dropping one, and only one, of its spikes (Elder Guardian Spike). This isn’t affected by looting.
I thought that combining three of these Elder Guardian Spikes and four
prismarine blocks/normal Guardian Spikes in a crafting table (the Elder Guardian spikes at the top and the prismarine blocks/normal Guardian Spikes in a T shape underneath) should get you a Trident. I think this is a much more deserving way of getting a Trident (more than killing an underwater zombie at least) as to get three Elder Guardian Spikes in the first place, you have to kill three Elder Guardians. The easiest way of doing this is still by conquering an entire Ocean Monument.
Here are some textures I made from Jappa's new carrot texture. Mojang, if you see this and decide to implement it into Minecraft I really don't mind if you use these textures. < Elder Guardian Spike
< Guardian Spike