My MChallenge Addon that adds some very nice challenges
Download it from Github
If you switch the chunk you get a random effect
If you take damage a random mob will spawn
If you kill a mob you lose a heart
If you attack an entity it will become a different a entity
If you attack an entity you get the damage as well
If you eat something you get damage
When you switch a chunk you get damage
You are not allowed to jump
Each level up gives you more hearts
If you take damage your/the servers inventory will be cleared
If you take damage you get a random effect