Oh wow, you have 666 subscribers :O EDIT [September 23, 2020]: I came back here just to tell you guys, the backsound is from Happy Tree Friends - Royal Flush.
Aww, nonono!! These guys don't use an app; they use a professional and complicated program for their animation that I don't think you'd be able to get your hands on with just a phone! It could even be an in-house software, which means that it's a program made by the studio themselves specifically for producing their own content, such as HTF, with it!
@@brokenrobot2004 Not to be "that guy" or anything, but it's just Adobe Flash, which everything in the video can now be done with Adobe Animate as well.