During the events of the Second Battle of Earth, and the flood ships arrival, most marines were caught off guard and unaware. Inside an oil refinery a platoon of troops were to hold out and protect all civilians inside. But then a new flood form arrived. The Catcher form. Most of the Marines fell to the onslaught of the tentacled monstrosities assaults, with only civilians and one staff sergeant to tell their tale.
The Flood Catcher Form is a collector of beings, housing them inside its masses of tentacles and later absorbed by the flood. It is a very good anti-vehicles and troop form, able to upturn large trucks (even buses) and slaughter troops without taking significant damage. They are very rare and few in number, but in the event of a Graveminds death they can all accumulate and form into a new one, although this has only happened once before the existence of the Flood in the Milky Way.
The long and sticky tentacles if the Catcher Form allows them to attack from afar and block many attacks, able to react not nearly as fast as an Onyx Sentinel but close. This forms primary purpose is a deathtrap, those surviving the tentacle masses usually having long term respiratory and skin problems, or just dying after their encounter. The most horrifying advantage though, is that they can use weaponry. The tentacles can pickk up and use most small weapons, like pistols, SMG, Sentinel Beams, and some Brute weaponry.
The problem with Catcher forms are that they take a lot of biomass to make, and are ungainly and bulky. Another thing is that they can't distinguish between prey, and when fighting with other flood forms, will suck them into their tentacles the same they would a grunt or brute. This terible cooperation makes it harder for them to fight because, they are pretty much killing their own back up.