Flood

On Quiffy's journey he was charged with collecting up the litter found in the caves, and could only progress to the exit once the level was clean.  However, Quiffy couldn't stand still for too long, a ghost of Quiffy's dead Aunt would trace his path through the level, killing him if they touched.   
 
Levels slowly filled with water from a number of running taps.  Levels would fill realistically, with water building and flowing into new spaces and creating air pockets.
 
Quiffy could collect a variety of weapons, including grenades, dynamite, a boomerang, a flamethrower, and shuriken, and required oxygen tanks to exist underwater for longer than a few seconds. 
 
The game had a perverse sense of humour, with bizarre teddy bear enemies, and the risk of weapons turning into rubber chickens at random intervals.
 
In a distinctly 80's attempt at copy protection, Flood was issued with a poster, and the game asked a random question about the content of the poster.