The Legend of Zelda: Link's Awakening has a bunch of Mario enemies in its side scrolling/platforming segments. Those segments are basically just Mario homages.
A few characters/enemies from other games also make appearances in the main 3/4 overview segments of the game.
Shy Guys,
Pokeys,
and Kirby.
Shy Guys and Pokeys made their first appearances in Super Mario Bros. 2, which takes place in Subcon, which is a dream world. Of course, Kirby lives in Dream Land.
Remember what else is a dream world? Koholint Island, the setting of Link's Awakening. I wonder if this was intentional.
Totally intentional references, culminating in the ultimate SMB2 reference: