Fishing in lava (New)

Custom fishing rods can be sort of tricky, but absolutely doable if you approach tasks in the right order. I would recommend the following:

• Create a small bobber entity in your model creator (if you're brand new and don't know where to start, I'd recommend looking into Blockbench, it's free and there are many resources available to learn it). It doesn't require any sophisticated animations, so making it as a basic modded entity should suffice.
• This entity should have an AI but no movement/combat/navigation tasks, just a behavior to float in liquids and be immune to fire and lava.
• Create a loot table for everything that can be fished out of the lava.
• Create a procedure for your bobbing entity that, on every tick while it is exerting the floating behavior, it has a chance to poll the above loot table.
• Create a tool object representing your new fishing rod, I don't know without trying to make it whether this tool should be off the fishing rod or multi-tool type, try both and see what works better.
• Create a condition such that, when the player right clicks with the fishing rod, it spawns the bobbing entity with some amount of tangential velocity + gravity to resemble throwing the line out. I have no idea how to attach a fishing line from the end of the rod to the entity, that's an exercise for the reader I suppose.
• Using another procedure for player tick updates and possibly another helper function tied to a right-click key bind, have it so that loot from the bobbing procedure are stored locally as item stacks. When the player right clicks again, the bobbing entity is despawned and the stored item stacks are added to player inventory.

This is a very off-the-top-of-my-head response so it might not all be accurate, but I hope it gives you a good place to start!