Well, you don’t come across this everyday fortunately. Cant say for sure it came down the plumbing vent, but its always a possibility. Critter Quitters are a cure for iquanas in the toilet.
https://www.mynews13.com/fl/orlando/news/2019/03/15/florida-man-calls-911-after-finding-iguana-in-toilet?cid=share_email