The Green Dragon Mask is a clothing item exclusive to former game moderator @Greenswe, awarded on the 14th of October, 2013. It is unavailable to any other player.
When worn, it spawns a green dragon which breathes green fire that replaces the player's punch. The item had the same benefits as the Dragon Hand and its variants: pushing other players farther and doing more damage to blocks. However, when worn together the effects would be applied twice, making it too strong, and hence those effects got removed.