Minecraft wiki entry for Creating_a_challenge_map, associated text: Use /give to "hack" stuff into your inventory. Monster spawners would be useful for some traps or funboxes (3x3x3 spaces with walls of spawners), or simply decorations. End crystals are elegant, but due to their obstructive and explosive powers, they can be used as sorts of obstacles the player has to safely destroy. (Check out the "Look before you Detonate" trap!)