The story
Canceled
According to The Art of 5th Cell book, "As of 2014, 5th Cell has shipped 21 titles and there are 23 unreleased titles/concepts we worked on to various stages of completion"
Scribblenauts Fighting Words, a puzzle RPG mobile spin-off of the Scribblenauts series, cancelled in 2016.
Anchors in the Drift, an action RPG game cancelled in 2015. Came back as a game with the same name but that also got cancelled. It is believed that Anchors in the Drift may have been reworked into Castlehold.
Scribblenauts Worlds, a 3D beat-em-up game cancelled in 2014.
Unnamed Scribblenauts Wii game, a Scribblenauts game for the Nintendo Wii had been in development around 2011 for about a year before Nintendo gave 5th Cell the Wii U, and Scribblenauts Unlimited was developed instead.
Unnamed Nintendo Wii Racer, a racing game planned for the Nintendo Wii system. Would have featured a similar mechanic to Sonic & All-Stars Racing Transformed allowing for vehicles to transform between cars, boats and planes mid-race depending on the obstacles on the course.
Unnamed Mobile MMORPG, a MMORPG in development for mobile phones, canceled in 2005 due to lack of funding.
Unnamed Nintendo Wii Dungeon Crawler, a dungeon crawler in development for the Nintendo Wii. Canceled for unknown reasons.
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Unknown PSP game, an unknown PSP game was canceled sometime in the mid-2000s in favor of 5TH Cell switching to the Nintendo DS since it was cheaper to develop for.
From Wikipedia’s article on 5th Cell, shared under CC BY-SA 4.0.4