Guthix's Blessing is an entity summoned to aid the player when using the ability of the same name. It will heal the player who called it for 8% of their maximum life points every 2 seconds, over a period of 10 seconds for a combined healing of 40% of maximum life points. It can be attacked and killed by any monster or player, (only when in a player-versus-player situation for players), causing the healing effect to end.
When using a multiple attack ability like Chain the player will receive a message in the game filter saying "You cannot fight other people's followers here.", preventing the player from killing their own butterfly. You can accidentally kill your own butterfly with Dragon Breath though.
Although the examine text claims it is Guthix's ghost, gods do not have ghosts or spirits that linger after death, as they explode into energy when they die.