Here's the model sheet I use for our sin Gluttony. If you need to get an idea of his biology and behavior, think of a T-rex on crack and that should be good. It literally eats anything, never being full and roaming the alleyways for things to eat. Including the trash cans its food is in.
Rather than make our sins instigators, it's more accurate to say that they suffer from their sin while also having an aura of influence. It's passive, but they seem to drag others down in their suffering