The voices in "Willpower Smurfs" are noticeably in a slightly deeper pitch.
In "Clumsy Luck", re-used animation from the Season 1 episode "The Smurfette" is used for when the Smurfs are mourning before Clumsy arrives.
In the syndicated version of "Clumsy Luck", the whole part with the Smurfs deciding on the choice of Clumsy's isolation before he accidentally sends Baby flying in the sky has been edited out.