Finally, a Sonic & Tails engine has been released with tails having separate collision to sonic's, as well as having his own AI to get back to you if he is or is close to being offscreen. There may or may not be a special action you can do in this engine Hint: It is triggered at some point when you use Tails to fly. Music: Dawn Dune Zone 1 from Sonic Nebula (to my knowledge, this is the only place where the music is shared publicly)
Press A to instantly teleport Tails to you. He does eventually come back on his own, but for convenience, you can also do that.