Scribble creature

When Chloe Webber was possessed by an Isolus, she drew a scribble with a pencil in frustration. The Isolus was able to animate the scribble using ionic energy, causing it to become a Scribble Creature.

History
The Scribble became a living scribble of graphite, animated with ionic energy. It hid inside a garage and when Rose Tyler opened it, it leapt out at her. The Doctor shone his sonic screwdriver on the creature, dispelling the ionic energy and causing it to retract into a small ball. While examining it in the TARDIS, the Doctor discovered it was made from graphite, which he demonstrated to Rose by erasing part of it with a pencil eraser. The Doctor and Rose were then able to work out that drawings were mysteriously coming to life. (DW: Fear Her)

Behind the scenes
In the DVD commentary to DW:Fear Her, writer Matthew Graham noted that, according to then-executive producer Russell T Davies, the Scribble Creature was never to be called a Scribble Monster, as the Doctor would never call anything a monster.