In Part 4, the Blue Yoshi that Peach rides to the graveyard protects her from the Big Boo that appears when she takes the 1-up mushroom.
The ending, with the whole of the Mushroom Kingdom celebrating, Mario and Luigi reunited, triumphant music, fireworks, and the final caption dedicating the series to all Mario fans new and old.
And then there's the sprites of Mario and Luigi back to back of each other, still the brothers they'll always be.
