The Flood are Halo enemies seen in World 9-6, The Library. They are the only enemies in this level and are also bosses (in the flood rush areas of the level). There are three types of Flood.
Flood Infection Forms: The weakest enemy of the Flood. Green ones die when you stomp on them, while red ones get stunned when you stomp them. They can be tossed like Koopa/Buzzy/Spiny shells when stunned.
Flood Carrier Forms: The transport for the Infection Forms. Stomping on them defeats them and gives you 1000 points, but five Infection Forms will come out! Only a POW Block can destroy a Carrier Form in one hit for good!
Flood Combat Forms: These enemies are twice the size of Mario. They take two stomps and when they die, they drop weapons. Despite being the toughest, they don't give out as much points as the Carrier Forms.