The Unggoy with Toys is an easter egg that can be encountered in Halo 2.
During the opening cinematic of Template:Levelname while playing on Legendary, at the very beginning where you see the Grunt, look closely at it and you will notice that he has a Master Chief doll and a Grunt doll in his hands. It is easier to see if you take a picture and zoom in with a editing program. If you have Halo 2 Vista, you can use the detachable cam.
On the other difficulties, he plays with other things. On Easy, he plays with a stick and dirt. On Normal, he plays with plasma grenades. On Heroic, he plays with fire.
The objects disappear shortly before the UNSC SOEIVs' landing on the surface of Delta Halo.
Gallery
A Grunt playing with two Plasma Grenades, as seen on Normal.