Johns and BabyJohns drop Immortality Shards which can be crafted in a 3x3 square into an Immortal Gem

This gem is used to make the Immortal Sword, which is basically an unbreakable Netherite Sword

It will also drop a John Tear, which can be combined into an Immortal Gem to create an Immortal Husk

This husk can then be brewed into Strength potions to make potions of Immortality

Immortal Gems can also be combined with Netherite ingots in order to make a Refined Immortal Gem

This gem, when held in the offhand and rightclicked with another armor/tool, will make the item completely unbreakable. The gem can also be combined with an Immortal Sword in the same way to make a even more powerful version of itself.

This gem can also be right-clicked onto an immortal gem block

Baby John:

• Spawns after 2-3 in game days
• Sometimes spawns in groups
• Drops xp bottles and rarely immortal gems when killed
• Will jump at players doing more damage
• May flee from players to heal when hurt too badly (unless following an alpha)
• Has an alpha variant that has more health and attack damage
• Any other babyjohns in the area will follow the alpha around
• Will always drop an immortal shard

John:

• Spawns after 4-5 in game days and 1000 blocks away form spawn
• Will stalk players if remained unseen
• Once a player is targeted, it will chase the player until either it or the player dies
• Can jump at players if they sit above it for too long, or teleport if the player escapes and it gets stuck
• Will drop immortal shards and sometimes a john tear used to make immortality potions