This is one of the few... maybe the only time an iconic D&D creature has changed because of an art mistake.
Up to 3e, I nominate the goblin. IIRC, In each version of D&D the little buggers got faster. This shows clear lines of evolution as the slower ones failed to live long enough to reproduce.
I do not think they got faster for 4e, showing the utter failure of either the system or the goblin to further evolve.
[*]3e: An artistic mistake (...this is true! It was a genuine mix-up between WotC art dep't and the artist!) gives the nycaloth two additional arms! They're now a 4-armed beastie, with two axes. This is one of the few... maybe the only time an iconic D&D creature has changed because of an art mistake.
[*]4e: More change, to nycademon (note: demon, not daemon). Fluff change - they're demons, not daemons or yugoloths. But, finally, 4e returns the nycademon to it's uber-power roots. The most powerful nycademon variants are higher level and more potent than either the ultrodemon or the raavasta (arcanademon). And, sigh, still four-armed. Due to an artistic error in 5e, I fully expect them to have six arms sometime later this decade.
And so far as 3.x not ever being certain what to do with the 'loths half of the time, let's not forget (or try to forget?) the battleloths, and the two super late 3.5 yugoloths who actually ignored the racial naming scheme (and most of the racial flavor text up to that point as far as I could tell): the voor and the corruptor of fate.
Most changed
Archons:
1e/2e/3.x = Lawful Good celestials
4e = evil elementals