Blow Hard did not originate from fanon, and the information on this page may not be entirely accurate to their canon. You may read more about this subject in the context of their canon on the following wiki(s):
Blow Hards are Pokey enemies that appear in the Yoshi's Island games. They stay stationary and constantly aim at Yoshi as he walks by. Blow Hards' main attack involves them spitting Needlenoses at Yoshi, which will damage him. A crosshair will always appear on Yoshi to tell when the Blow Hard is about to fire however. They are near-invincible, though Yoshi can stun them by ground pounding or throwing a Yoshi Egg at them. By breathing fire or breathing ice then breaking them in their frozen state, Yoshi can permanently defeat them.
Throughout the Yoshi's Island games, several more Blow Hard types have appeared. One of these types are Hanging Blow Hards, which allow ropes for Yoshi, with the help of Baby DK to climb, though produce Needlenoses that can damage Yoshi if he hangs on for too long. A second type, Drool Hard, hangs from the ceiling as it spits out Needlenoses, which bounce along the ground and explode after a short time.
Blow Hards make an appearance in Stampede Breakfast 2 as an assist character. When summoned, it will appear from the ground and act exactly as it does in the games; aim at opponents and fire Needlenoses that travel forward and deal damage and knockback. If one attacks the Blow Hard hard enough, it will be stunned for a short time.