Scribble creature

The scribble creature was the product of Chloe Webber's frustration, in which the savage drawing she made was animated by the Isolus using ionic energy.

Biography
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 Tenth 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 worked out that drawings were mysteriously coming to life. (TV: Fear Her)

These creatures could be found attacking the Doctor inside the drawing that Isolus trapped him in. (GAME: Art Attack)

Behind the scenes
In the DVD commentary to 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.