Comet Observatoryさんのイラストまとめ

In Super Mario Galaxy 2, if a Smeech touches Yoshi's lips and then the player collects a star, the Smeech will still be attached to Yoshi when the animation plays.

Two images of a UFO can be found in Super Mario Galaxy's particles.jpc file.

They are used in-game during the first prologue cutscene, but considering said cutscene is a pre-rendered movie file, that leaves these images as leftovers.

Discovery by @CometMedal.

Super Mario Galaxy received Game of the Year in 2007 from IGN, GameSpot, Kotaku and Yahoo! Games. Australian magazine Hyper also named Super Mario Galaxy as Game of the Year in 2007 as voted by its readers.

The spike ball move used by Bowser in the last boss fight in Super Mario Galaxy (left) returns in Mario & Luigi: Bowser's Inside Story (right).

Early concept art of Rosalina as seen in the Collector's Edition of the Super Mario Galaxy PRIMA Official Game Guide (left), final concept art of her (middle) and current design (right).

Mario Kart Wii is home to various Super Mario Galaxy Easter Eggs.

Rosalina can be unlocked by having save data from Super Mario Galaxy.
The Rainbow Road course is full of Star Bits and a portion of its music is based on the Good Egg Galaxy's theme.