Monsters in the Arena are rated by difficulty. See the chart below.

Monsters and Their Ratings
Monster Difficulty Method
Zombie Easy Melee
Zombie Pigman Medium Melee
Enderman Hard Melee
Creeper Medium Combustible
Blaze Hard Ranged
Silverfish Easy Melee

Cave Spider

Hard Melee
Spider Medium Melee
Skeleton Medium Ranged
Magma Cube Medium Melee
Slime Easy - Hard* Melee
Witch Hard Ranged
Giant Hard Melee
  • Depends on size of slime.