add spear traps and super dart traps that go crazy everywhere. Oh, and a bunch of healing stuff like statues, honey, campfires and lanterns, then you'll have yourself an afk arena
Not to mention, super dart traps don't crit.Using spear and dart traps at the same time is a bad idea, because of how invulnerability works.
Also, DicemanX already created a fully AFK arena: