And you thought eatin' shrooms to grow bigger was strange. How about this: flying green crabs dropping red clay bricks on a grinning, toothy duck wearing a cape and glasses with a double-barrel shotgun coming out of his mouth.
At least it's set in a pond, so the backdrop isn't too fanciful.
The game is Deadly Duck for the Atari 2600, a 1982 shooter title published by 20th Century Fox. I've played it, and it's not too bad. It's a vertical shooter, similar to Space Invaders and Demon Attack.
You play as a duck striving to gun down flying crabs that drop bricks on you — actually, around you. When the bricks land, they temporarily impede your movement to the left or right, then disappear in a few seconds.
This is one of the many vintage video game box illustrations that rendered the typically absurd and abstract situations of extremely low resolution games in a very realistic and literal manner. Super Breakout for the 2600 is one of my favorites (it also inspired a 2006 Halloween costume suggestion).
You can find many more examples of this curious art form on the web, including many parody boxes, so watch out for fakes.