Kyutai Panic Adventure Returns!

Specials screened at special events. Kyutai Panic Adventure Returns! was screened at an event named Odaiba Boken-Oh featuring characters from Dragon Ball Z, One Piece and Kochira Katsushikaku Kameari Kouenmae Hashutsujo while Shingeki no Kyotou was screened at the Tokyo Skytree featuring characters from Attack on Titan. 

Both are crossovers between two or more different anime with short episode(s). While Kyutai Panic Adventure Returns is more shounen (One Piece/Dragon Ball), Magica Quartet x Nisioisin is more comedy centered (Nisemonogatari/Mahou Shoujo Madoka Magica). 

Both are crossovers between different anime. While Kyutai Panica Adventure Returns is more shounene-centered (One Piece, Dragonbal), CLAMP in Wonderlan is mashup of anime made by CLAMP (Tsubasa Chronicele, xxxHolic, Chobits...). Both have short episodes. 

Both are crossovers between different anime. While Kyutai Panic Adventure Returns is shounen-centered (Dragon Ball, One Piece), CLAMP in Wonderland is crossover between anime made by CLAMP and is more like a music video.