The Graske appeared in the Doctor Who mini episode “Attack of the Graske”, this episode was a special interactive episode which aired on the red button service after “The Christmas Invasion” aired on Christmas day.
The Graske come from the planet “Griffoth” and are very small aliens. Griffoth was seen on the Tardis’ Monitor in “Attack of the Graske”. (Can be seen above)
The Graske invade planets by replacing the population. Keeping the real lifeforms stored away that they have snatched and make clones of them. The clones then are sent back to replace the original lifeform as if nothing has even happened. The Clones are called Changelings, whose eyes often glow an eerie green.
Graskes can teleport from place to place using a transmat device where they then snatch people or other creatures using a small gun they have. This gun sends out a spark, producing a blue aura around the victim. (Can be seen below.)
The Legendary planet Griffoth is where all the victims who have been snatched are being hidden. To get inside the Graske’s base there are a lot of puzzles you will have to solve. Secured with different locks it’s a hard base to enter. In the episode “Attack of the Graske”, you play The Doctor’s companion. When you and The Doctor manage to get through all the tricky puzzle combinations you are left with one decision, that being which button do you press? If you press button 1 you reverse the settings, destroy the duplicates, free the prisoners and teleport them from wherever in the Universe they were snatched from. If you press button 2 you freeze everyone and everything there. The two buttons can be seen below.

I chose button 1 which was the right thing to do, to teleport the prisoners of the Graske back to where they came from.
The Graske still live on the planet Griffoth, they have an opportunity to come back in a new Doctor Who adventure, as they weren’t killed.