Super Mario Land (Game Boy, 1989) 
As we look back upon it now, Mario's first Game Boy outing might seem to stand starkly out from the norm. But remember this;
Super Mario Land was released in a time in which
SMB 3 had yet to solidify the Mario franchise formula. At the time of
SML's release, Bowser and his now-recognizable minions had appeared in just one game, Princess Toadstool had been kidnapped naught but once, and Mario had just come off of throwing Wart for a loop the previous year in a game that differed drastically from the original
SMB. With this in mind, it doesn't seem so strange that the creative team behind
SML should have seen fit to deliver us a new villain, a new damsel in distress, and a new cast of bizarre enemy characters. This was, after all, back when Mario's fans didn't automatically know ahead of time what their hero's next adventure would be about.
Super Mario Land introduced many novel concepts that, for better or worse, have yet to be reused. Such concepts and novelties include the Sky Pop Airplane and Marine Pop Mini-Sub, the Super Flower that granted Mario the ability to throw bouncing "superballs", and of course Tatanga, who, in this fan's opinion, is long overdue for a return.
SML is also notable for serving as the debut of Princess Daisy, though it would take Nintendo more than a decade to find further use for her.