Les Sept Boules de cristal
Hergé asked him to remake two of "The Adventures of Tintin" – "The Seven Crystal Balls" and "Prisoners of the Sun" – into a script for one long animated movie, "Tintin and the Temple of the Sun". He also wrote the script for "Tintin and the Lake of Sharks". Greg was asked to write two stories for the Tintin comics as well, including "Le Thermozéro", but in the end Hergé, wanting to keep all creative control, did not use them.