Bubonic

 The 'black death' was the deadliest pandemic in recorded history, and now in your Minecraft world. This is a very simple and straightforward mod, stay away from the plague to survive. Infected mobs will have black skull particles around them and approaching just a few blocks away is enough for you to catch it. During world generation, there is a rare chance for an animal mob to spawn with the plague. At night, zombies have a much higher chance of spawning with the infection and spread it to nearby mobs. For everyday you have the plague, it will only worsen with day 1 being "harmless". By day 2, it will start to kill you making it almost impossible to survive days 3 to 4. On day 5, you will die. Your only hope is eating an enchanted golden apple which will instantly cure you. Milk will not save you. Can you survive the plague on a hardcore world?