The Inside Scoop is not as simple as adding a shot of Jagermeister to the classic childhood drink (though that isn't a bad idea). It's a little more complicated and, shall we say, sophisticated than that.
The drink begins with a misting of Chartreuse in a tumbler, then builds the liqueur, root beer, and ice cream in normal float fashion. It is then topped off with root beer bitters and an expression of orange oil. The first and last steps are small, but they are essential to bringing the drink to a new level of flavor and they are easy enough to do that it is worth the little bit of extra effort.
For the bitters, there are a number of recipes online for homemade root beer bitters and one of the best commercial options you will find is the Sarsaparilla Dry Bitters from Bad Dog Bar Craft.