This is similar to the Sneak Attack + Gandalf combo. You don’t get a bevy of additional options like Gandalf. You do get to use Beorn’s strong combat stats for the entire phase. He has hero level defense and more hit points than any hero other than his own hero version. He can block and most likely survive to return to your hand. If you don’t need him to block, you can activate his action ability to attack for 8. Then you can return him to your hand thanks to the resolution of Sneak Attack and Beorn’s ability both of occurring at the end of the phase. When effects would occur simultaneously, the first player gets to choose the order of resolution per FAQ 1.02.