I think that all Sploder series take place in the same universe. I know I did this on the Sploder Series wiki, but there is so much more info. I am going to avoid obvious crossovers like Sploder Deadlocked and CPX for this.
I am going to start with the Skyward series here. There are several cameos in these games, so lets start this here. In Level 3 of the original game, a ghost-like figure can be seen peeking behind a rock. If you have played Petit, you will probably recognize that as a Muha Kid. Professor Dunce from The Mjduniverse Series can be seen in the last level of Skyward. In Skyward 2, he makes another appearance as a teacher in a school-like structure with Zack and Jack in it. Jessica from Catlorful can be seen in level 1 of Skyward Revelations, too. Desert Wolf along with Tigzon can be seen in Petit Lost in a Cave, and Puffies appear in Petit's Adventure, also. In Tigzon, various crates can be broken, and inside some of them, you can find Mario or Sonic, which connects this realm to existing video games.
Actual Sploderians have appeared in Cube Fighters 2, where a DealWithItDewott logo can be seen on one of the buildings. Also Desert Wolf appears near the DWID building. The urban envirorment of Cube Fighters 2 is filled with several easter eggs. Dealwithitdewott appearing in Cube Fighters 2 connects this universe to the world of Sploder movie series. Various members being in multiple of these pretty much connects the whole universe of Sploder movies.
Even cancelled Sploder series characters have made cameos. Polvo appears in both released Skyward games and Texx, well, Damage Dux. He was originally in one of Mangamixer's old games, and later he moved to Texx, and he also appears in Tigzon Battle, connecting two Mangamixer games and one cancelled one. FEEL FREE TO ADD MORE