The Game: The sky is falling! Or so it seems. As this game is subtitled “A Space Nightmare,” you’re not battling aliens here, but ever-descendig and evading waves of such ordinary items as bow ties, hamburgers, dice, and so on. Unlike so many other Space Invaders variations, you won’t die the moment the attacking forces reach ground zero – but you could, if they slide horizontally right into you. (Activision, 1982)
Memories: Activision, much like the Odyssey 2 game designers, always knew how to put enough of a twist on game with an established “formula” to keep the litigious wolf from the door, and this is another classic example of that – not to mention an annoyingly addictive little game.
In Megamania‘s case, the arcade inspiration was a relatively obscure coin-op called Astro Blaster, from which this game borrows the attackers’ 
patterns of movement, but that game was a relatively tame one involving attacking spaceships. By changing the nature of the opponents in Megamania, Activision probably kept most people from making the connection.