G.I. Joe (Orca and Wolf Transformations)

This is a famous transformation, but I think Daymon is right to recommend posting it anyway.
It's from the season 2, episode 15 of the original G.I. Joe cartoon, titled "Iceberg Goes South."
Cobra ("a ruthless terrorist organization determined to rule the world!") is creating beast-men in the arctic, and Iceberg, one of the Joes, gets captured and transformed into a killer whale. I'm old enough to remember watching this episode when it first aired; this was one of the first transformation scenes to make a big impression on me as a child. 

Every time I try to embed the same video multiple times and with different cues, Youtube keeps fucking up the cues, so I'll have to give you cued links to the next scenes. So here's Iceberg's reversion to humanity. Lastly, here's one of Cobra's human-animal hybrid soldiers reverting from wolfman to plain man.

EDIT: Every available video of this episode seems to be severely cropped. I'm going to look for DVD-quality source material and will re-present this episode in a future update.