Rally blade
The Rally Blade is a feature that lets players toggle allowing other players to randomly teleport to them.

Rally Blades appear at the spawn of adventure worlds in the Outpost of Light at the bottom level. One also spawns in Journey's Beginning.

Players can press the "E" key to teleport to a random player, in their current world, that has Rally Blade activated.

Holding "E" allows the player to toggle allowing/disallowing random players to join. Players on your friends list will still be allowed to join your game, and /joinme username will still work, even with this disallowed.

It is useful for challenges to join someone in the right biome.