Final answer:
The Blast-Ended Skrewt was encountered during the Third Task of the Tri-Wizard Tournament, as one of the obstacles in the maze.
Step-by-step explanation:
A Blast-Ended Skrewt was encountered by participants during the Third Task of the Tri-Wizard Tournament in the Harry Potter series. This treacherous maze challenge was the final task, where champions had to navigate through various obstacles, creatures, and enchantments to reach the Triwizard Cup. The Blast-Ended Skrewts were among the magical creatures that added to the peril of the maze.