In my humble opinion the antagonist in "Night of the iguana" would be the *human condition itself.
The Night of the Iguana - 2006 SUSPENDED was released on: USA:2006
Ava Gardner
Tennessee Williams
Cousin Skeeter - 1998 Night of the Iguana 3-5 was released on: USA: 11 February 2001
It's a Living - 1980 Night at the Iguana 4-6 was released on: USA: 1 November 1986
the night of the iguana
Hollywood and the Stars - 1963 On Location Night of the Iguana 1-22 was released on: USA: 24 February 1964
It Was A Film Set.
Four Kings - 2006 Night of the Iguana 1-7 was released on: USA: 16 March 2006 UK: 27 October 2006
Twelfth Night and indeed most of the comedies do not fit well into the protagonist/antagonist mode of analysis. Viola is the main character in the play, but there is no other character who particularly stands in her way.
Iguana is a genus of herbivorous lizards native to Central America. There are two species of iguana, Iguana delicatessima (Lesser Antillean Iguana), and Iguana iguana (Green Iguana). There are several similar genera that are commonly referred to as iguanas.
For that matter, who is the protagonist of A Midsummer Night's Dream? Oberon? Bottom? Lysander? Hermia? It is not a play which lends itself to analysis using the protagonist/antagonist paradigm. The best answer is simply that there is no single Protagonist or Antagonist in the play. In every scene, different characters balance and contrast with each other.