Bacteri-Yuk is a Commander Keen Fangame where Keen spends his time destroying bacteria and viruses while microscopically small. It consists of a number of levels, each reached either by entering a password, or completing the previous level.
Graphics are rather good, and gameplay isn't hampered by many bugs, apart from the usual CNC problems. It is however rather slow, and it does not support saving games. The range of monsters Keen faces is inventive including dinosauroids and walking hamburgers. It can be beaten rather quickly once you get the hang of gameplay.