Tower suggestion: Contained creeper
"Contained creeper" would suck in all creeper [C and AC] and once it fills its internals with C it would close down. The insides would not melt down immediately due to contact with C because it could be made of a material with AC plating [AC is a liquid, so it follows states of matter logic, right?] and when it closes down because it has too much C, it would begin spraying all the C with AC.
Great as a "shield" as it absorbs all the C before it can get to towers
Terrible as something that actually attacks, as by sucking in C, it is either now bringing C closer to your base, or it's dead because the outsides were overloaded with C