(Note: english is not my first language)
1) The summoning Item
Add a craftable item (from now on referred to as "item") that can be used to summon a boss.
Also add some specific requirements for the item to work, for example the item only works at night, and some minecraft vanilla "advancments" must be completed. This is meant to prevent the player to fight the boss too early when they are not ready for it.
The item should also have a "no requirements" version, so that players can fight the boss early if they want. This version of the item would be found in the overworld dungeon chests (as common as possible) and village chests (only rarely).
2) The Boss
As soon as the item is used, the boss will spawn at a distance of 20 blocks from the player. The boss itself is just an Illager with a custom AI and 250 HP,
he is immune to lava damage (but not fire), suffocation and drawning damage.
The boss will keep moving slowly around the player while trying to mantain the same distance, and every 4 seconds will perform one of the following actions:
- shoots a blaze fireball at the player (20 seconds cooldown),
- shoots an explosive ghast fireball (32 seconds cooldown),
- shoots three full speed arrows in quick succession (12 seconds cooldown),
- pushes away all entities and players in a 10 block radius, with the same power of the enchantment "knockback" level 3 (20 seconds cooldown),
- spawns a spider jokey in a 5 block radius from itself (16 seconds cooldown),
- spawns a chicken jokey in a 5 block radius from itself (16 seconds cooldown).
3) The Reward
The Boss will drop some amount of experience, possibly many times the amount that a normal hostile mob would drop.
Most importantly, he will drop a custom reward that can be used in many crafting recipes, such as a fast furnace that does not need fuel to run but smelts faster if provided with fuel, a crafting table that remembers the last crafting operation it was used for and can store ingridient to auto-craft it when receives a redstone pulse, or a magic lead that can capture and store any tipe of non-hostile mob and release it on command.
Let me now if you are interested in creating this mod, i can't pay for it but if anyone wants to try and make it, i'll be happy to test it.