Twelfth Night is based on the prose tale of "Apolonius and Silla" in Barnabe Riche's "Riche his Farewell to Militarie Profession" (1581). In assessing the extent of aggressive comedy in Twelfth Night it is important to look at the source material. The character of Orsino in the original was a jealous brute, shutting Viola away. We see Orsino become jealous in Shakespeare's version but he does nothing anywhere near as bad as his actions in the original. Also, Sebastian leaves Olivia with a child in Riche's version. These undertones show that Twelfth Night is based upon a turbulent story. Shakespeare manipulates this tale and takes out of it what he needs, converting the prose into a Romantic Comedy. Partly due to the original story line the play has an aggressive edge; while keeping in the realms of the Romantic Comedy genre. What happens in the original directly influences the way in which Shakespeare writes the play and the things he changes are just as important as the things he leaves unaltered when assessing the extent of aggression in the comedy.
One of the things that Shakespeare leaves unaltered is the threat by Orsino to kill Viola in a jealous rage. This can be left in because the threat is not carried out. It is important to remember that although there was an intention by Shakespeare to have an air of conflict in the play it was a festive comedy to be shown to Queen Elizabeth on the Twelfth Night of Christmas.
The light-hearted humour with an aggressive edge is evident during the sword fighting we see in the play. It is important to note that it ends without bloodshed; which is typical of sword fights in Shakespeare's Romantic Comedies. The sword fight gives Twelfth Night aggressive comedy in the literal sense of the phrase. The comedy comes from pitting a man and woman together in combat; the aggression comes from the potential fatalities which could occur.
The comical elements of this play do tend to have an extra edge to them.