To even begin to write about comedy, we have to start with what Sir Philip Sidney wrote. To my best understanding, it is that comedy is often riddled with the most ridiculous/exaggerated of common problems, but shows that there is no black without the white – comedy articulates the power of virtue that is compared, side-by-side, with the filthiness of evil.
Using this idea with The Merchant of Venice, I found three passages that do/do not illustrate the writings of Sidney.

Act 3, Scene 1:
Shylock, who is the moneylender, is possessed with rage. His daughter had fled and his money stolen/spent. The underlying idea in the play is that Shylock is mistreated or not taken seriously for being a Jew. In his brief monologue (lines 45-60), Shylock mocks how Christians handle ordeals such as revenge, and thus assures the audience that he will inflict Christian example upon Antonio. The irony/comedy in this is that his daughter had fled to become Christian, his money had been taken and lost by a Christian, so then too must Shylock extend his own sense of Christianity – this sort of comedy makes it amusing to watch Shylock struggle in his attempt to punish others, but contrasts that he too is misrepresenting a religious disposition (and also causes the audience to be suspicious or disliking of Shylock through his behavior).

Act 3, Scene 5:
Lancelot harasses Jessica about being Jewish. The comic contrast to this scene comes at line 17, where Lancelot contrasts about how doomed Jessica is to have a Jewish heritage, but also exclaims that Lorenzo converting Jessica is a crime, because the more Christians they have, the higher the price of hogs.

Act 4, Scene 1:
The trial starts out with no comedic value as per Sidney. There are no virtuous ideals, only the villainous desires of Shylock (lines 34-101). However, when Portia arrives disguised as Balthasar, the tables turn. We can imagine Shylock’s face deprived of color as Portia places him in a spot where he must die by the law. The contrast can be seen that the once blood-thirsty Shylock is now cowardly and must beg for mercy from the Christians that he had believed to be merciless before.