There are a lot of people who are barely here. The ones that bother me most are the ones who show up periodically as mafians don't normally stay completely inactive. They would be:

Plum
Edgeworth
Lamiroir
Apollo Justice
Trucy Wright
Wesley Stickler

Naturally they aren't all definitly mafia, but I'd like to see and hear them more. The bolded ones have my attention because of either poor play, or taking others reasoning.