Bukkit

/fall <player> - Drops the player from y256.

/herobrine <message> - Displays a message from Herobrine.

/nausea <player> - Puts Nausea on the player for 20 minutes.

/halfheart <player> - Drops the player down to half a heart.

/creep <player> - Creep the player out by playing a modified nether portal sound.