When driving to the consulate for the first time, Jim Carrey forgot his lines, so instead started singing the theme from the movie Chitty Chitty Bang Bang. Both actors stayed in character and the director loved it so they kept it in.
According to Simon Callow, Jim Carrey didn't really want to make the film, which made on-set experiences awkward.
Despite Jim Carrey only doing this movie due to contractual obligation, the studio attempted to get him interested in doing another Ace Ventura movie several times throughout the years, to which he declined. As such, the animated series Ace Ventura: Pet Detective (1995) and sequel Ace Ventura: Pet Detective Jr. (2009) were notably made without Carrey's participation.
Jim Carrey spent a lot of time off sick, which affected the contract of actor Simon Callow. Callow's contract had actually expired before he could finish filming his scenes. Despite this, he wasn't paid overtime as Carrey's illness was regarded as an "Act of God" in the contract, which Carrey himself claims as "unfair". Because Callow already had other commitments in London, the producers suggest he flew back regularly in first-class, as the contract had stated. It wasn't until later that Callow found out that the producers were deducting the cost of his plane tickets from his overall salary. In his words, he "finished up working almost for nothing".
According to Jeff Daniels, Jim Carrey had explained to him the reasons why he didn't like the sequel much. He disliked the whole "Ace is afraid of bats" angle, as he found it to be cheap, and even fought with the director about changing the script so that Ace was merely allergic to bats. Carrey was also very nervous about the film's depiction of the native characters, and that people might take offense to them. He's even surprised the film hasn't been outright banned.