Clom

Clom, also spelt Klom, was the twin planet (or sister planet) of Raxacoricofallapatorius.

History
The inhabitants of both worlds were similar in physical characteristics and were both members of the Raxas Alliance, along with Clix and Raxacoricovarlonpatorius, but despised each other. (DW: Love & Monsters, SJA: The Gift)

The "Abzorbaloff" was a native of Clom. (DW: Love & Monsters)

Clom was used in an oath by a Slitheen as "for the love of Clom". (SJA: Revenge of the Slitheen)

Land Prawns were a popular delicacy on Clom and was also enjoyed by Raxacoricofallapatorians. (SJA: The Gift)

Along with many other planets, Clom was stolen by the Daleks and taken to the Medusa Cascade in 2009 as part of Davros's plan to detonate the Reality Bomb. This was stopped by the Doctor and the Children of Time, who sent Clom and the rest of the planets back to their proper places. (DW: The Stolen Earth / Journey's End)

At some point, there was a Disneyland on Clom. Whether this indicates later human contact with the planet or the borrowing of the concept by the natives is unknown. (DW: The Girl Who Waited)