Kirby: Right Back At Ya! "Shell-Shocked" (found English dub of anime episode; 2005-2006)
A screenshot from the episode.
Date found: 26 Sep 2015
Found by: Operation Hoshi no Kaabii
Kirby: Right Back at Ya! is an anime series based on the Kirby franchise. Over the course of the series, Kirby and his friends fight to bring down evil emperor Nightmare, all the while evading King Dedede and his assistant Escargoon, who try to get rid of Kirby using numerous monsters provided by NightMare Enterprises.
The 88th episode "Shell-Shocked" was centred around Escargoon's shell breaking and turning him into Maimaigoon.
The episode aired on June 11th, 2005, but it was pre-empted by "This Week's Baseball" near the end for unknown reasons (it is still currently unknown if it officially aired anyway or not in markets where 4Kids TV and the remainder of Fox's programs were seen on separate stations due to the main Fox affiliates in those markets refusing to clear 4KidsTV, though comments suggest that it was preempted in those markets as well). The episode didn't fully air until 2006 and was ultimately lost until YouTuber "Operation Hoshi no Kaabii" uploaded it on September 26th, 2015, but it was later taken down by Nintendo.