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Cobalikbot Acorn Delta was a rogue robot that made illegal modifications to itself and posed a threat to the whole universe. It was imprisoned beneath a replica of the Eiffel Tower on the planet Cobaltikar 45 and held using the energy from the universal atmosphere – an energy drain that threatened to reduce the planet to dust. Acorn Delta was free for a short while because of the Eleventh Doctor's intervention before being trapped beneath the Eiffel Tower when it was weakened and collapsed on top of it. (COMIC: Tower of Power)