Meet, the Devourer:

Technically not a 'combat form' per say, but it does help continue the Flood's battle in it's own way. this thing goes around picking up body parts, small animals, etc (anything organic that can fit into it's mouth that is not plant life basically that cannot be turned into a combat form) that can't be made into a 'proper' combat form and converts them into infection forms, which it then barfs up to continue the infection. When attacked directly, it will fight back by spewing out infection forms and whipping at them with it's tentacles. If it can, it will try to eat the attacker, piece by piece, if necessary. When defeated, it explodes into a shower of infection forms much like the carrier forms.