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"Pocoyo" had many pilot episodes made in Spain in 2003-2004 before the show premiered. In the pilot episodes, Pocoyo has a yellow pacifier in his mouth. Which is something he formerly had in the final series. And also the narrator is an American female in the pilot, and was later redubbed by a British male. This pilot is found, however, there was another pilot which remains partially lost. It was shown on Cartoons on The Bay 2006. https://www.awn.com/animationworld/cartoons-bay-2006-10-years-celebrating-tv-animation
Concept art of Pocoyo. (FUN FACT: At the time this was drawn, Pocoyo was just called 'The Boy'.)
Loula prototype design, originally as a male character named Lucas.
Model references for Ducky.
Possible later character designs, notice that Elephanta/Elly has no tusks but retains her fingernails and toenails and Duckie/Pato is slightly closer to the final design.
A book of the 1st pilot.
Prototype whale and prototype places.
A gif from the 2nd pilot.
A screenshot of the 2nd pilot. Notice the difference in Ducky's legs.
A GIF from an unknown animation, possibly just an animation test.
Pocoyo's original 3D model.
Sleepy Bird mentioned as "Lazy Bird" in the pilot.
Unknown screenshot. It's confirmed by the official Pocoyo Twitter account that the image right here is from "Pocoyo's Story".
A photo comparing the old models to the current ones.