As the play is replete with duos and trios(see Sonnet 42 regarding this point), one might choose two or three co-heros. Salerio is one contender too often overlooked. Editors can't seem to agree whether he is one or two characters because of various spellings in the text(one even suggested that there are two Salerios). He seems to be a trusted employee of the Duke and speaks to most of the other characters at some point. Shylock likes him enough to tell him exactly how he feels(3.1). If he seems a bit rude in suggesting that he is fond of Jessica, an error of that sort is common. My first suggestion seems consistent with the idea of regarding Antonio and Shylock as co-comic villains.
You could answer Portia because she pleas for mercy. By pleaing for mercy, she stops the evil cycle victim becoming victimizer, (Shylock) in the play. Without mercy, the cycle, fueled by revenge, never runs out.