Many game companies in the 1980's held contests in an attempt to boost sales of their games and give their fans something fun to compete for. "Defend Atlantis" was one such competition, run by a company call Imagic.
Unfortunately for Imagic, there were a lot of good Atlantis players. In fact, more than a handful of individuals maxed out the score, so Imagic had to figure out a way to decide who the top four would be. They created a special contest version of Atlantis, which they called Atlantis II, that the top scorers would use for a tie-breaker. Atlantis II is basically the same as Atlantis, except that it's faster, harder, and lower scoring.
see Atari Age for full story
Low and behold one of these cartridges "appears" to have turned up on ebay, whether such a game warrants a $50,000 price tag, I'll leave up to you to decide
Atlantis II on ebay
for collection only in US