Nintendo Characters Sleeping
Link Catching Some Z's
Sleep at the Inn at Rose Town. When Mario wakes up, Link is there sleeping! He doesn't talk to you, but if you try, the game plays a familiar Zelda sound.
Samus Catching Some Z's
Check out the Guest Room in the Mushroom Kingdom Castle after getting the 5th Star (She only appears at this time. If you try to progress too much further in the game, she'll be gone)
Credit goes to: http://www.rpgclassics.com/shrines/snes/smrpg/secrets.shtml