Something fun I just realized, look at the Wario team logos in the baseball games:
http://www.mariowiki.com/Wario_Greats
Notice something? They all use the same font as the Land 2 & 3 title logos:
Why yes, I am a nerd. Thanks for asking.
Wario appeared in G&W Gallery 2 and 4 (both numbers are even numbers)
Speaking of the game, a few items from Wario Land also appear:
In the other game, it seems Wario is holding the Golden Hammer from Wrecking Crew, defending his statue...