From recent memory?
Alt. Rodimus was missing one of his guns (DAMN YOU Q.C.!) and Movie Arcee had no paint on her face.
DN

 

Oh, really. I never knew that. Awesome.

I remembered one. I bought an Alt Swindle (red box) that was missing his head. I'm not sure if he was a really carefully repackaged return, or if it was a factory error. It was returned, I didn't bother getting another. I didnt care much for the mold.

 

Classics grimmy has two left hands. Classics starscream didn't come with one of his chest rotors/landing gears.

 

I have a G1 Goldbug with two right arms, got it new back in the day. While i knew it was wrong I kinda liked it cause it made it look like he has one arm raised up in bot mode. Since the throttlebots have no articulation it was ok.

My Classics Hot Rod has missing paint from one shoulder.

 

My TFTM 2007 Deluxe Bonecrusher has red eyes, but is missing the rest of the paint on his face.

 

They released two versions of that figure in the states, RHD and LHD. It is a variant, not an error.

 

My Sams Club Battle damaged Prime set came without instructions and missiles for Starscream.

Other than that I've never had any bad QC issues other than a few with minor poor paint applications.

 

Urban Camo Ruination packaged with two left combiner fists. Other than paint mistakes, that's all I've ever run into

 

Mine came with two left feet.

 

You better not take it dancing, then  

 

I got a Cybertron Evac with to right hands.

 

they dont give me transformers for free!

 

As Valkyas pointed out, those heel things aren't supposed to come down like heel spurs. They're detail parts for accuracy to the design, as seen in this picture: