It's common knowledge that a sequel has to be more spectacular than the film that came before it, which is one of the reasons people are starting to worry about the Marvel universe (saving the world from imminent destruction three times a year seems a bit much). But for animated movies the formula has a different twist: just add some new characters.

Rio 2 Jesse Eisenberg Anne Hathaway
Will The Success Of The Original 'Rio' Be Crowded Out By The Introduction Of New Characters In 'Rio 2'?

This also presents a problem, as sequels tend to feel increasingly crowded as the expanding cast of characters jostles for screen time. From Toy Story to Shrek, animated ensembles get bigger and bigger as they go along. Sometimes the filmmakers find a character so popular that it gets its own spin-off movie ('Puss in Boots'), and sometimes what started as a smaller side character grabs the spotlight from the progressively crowded main cast (Ice Age's Scrat or Madagascar's penguins).

Rio is only just starting down this road, but the signs are there. For Rio 2, the filmmakers felt the need to bring back the vanquished villain Nigel, the vain cockatoo voiced memorably by Jemaine Clement, and this time they've given him a sidekick who's even more of a scene-stealer than he is: a poisonous frog voiced magnificently by Kristin Chenoweth.

Read our review of 'Rio 2.'

Other new characters include Eduardo (Andy Garcia) and Roberto (Bruno Mars), the father and ex-boyfriend of Anne Hathaway's lead parrot Jewel. There are also Blu (Jesse Eisenberg) and Jewel's three burgeoning-adolescent chicks.

So that's at least six new characters who will have to be back for Rio 3. And presumably Tracy Morgan's slobbery bulldog Luis will want more screen time after being sidelined this go-round. Yes, it's a jungle out there.

More: Check out photos from the 'Rio 2' premiere.

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