In 2003, mahq.net made an April Fools' Day prank announcement of a Mobile Suit Gundam SEED sequel, which some websites in Japan apparently thought was a genuine one. And when Mobile Suit Gundam SEED Destiny was released, the uncanny similarities just made it funnier.
In 2016, Toho announced a crossover movie between Godzilla and Neon Genesis Evangelion... which turned out to be a promotional stunt for Godzilla Resurgence (which makes sense, considering who's directing that movie).
The flip-flop was lampshaded heavily on both shows: Jeopardy! had Wheel-themed categories in the first round such as Buy a Vowel and Before & After, which later became a recurring category on Jeopardy! itself, and fool-themed categories in the second, and a Final Jeopardy! category of Trinidadian Amateur Ichthyologists. Wheel had several gag puzzle
The gay-themed channel LOGO had a whole ad campaign about The A-List: Amish Country. Granted, it fooled no-one and was more intended as a parody of the series.
an impressive amount of detail went into the making, complete with CGI monsters, music taken from the games, and a complex storyline expressed in three short minutes of filming. The only clue to its status as a hoax was the purported release date for the actual movie %u2014 April 1, 2009.
The announcement that there was going to be a Magical Girl anime Spin-Off of The Powerpuff Girls was presumed as an April Fools joke due to being announced on said date.