Well, this little fella is!
I present to you: Kneecappa, the favorite Grot servant of Morgrub Nazblitz, da Flash Dregga, Warlord of Waaagh Nazblitz. Warlord Morgrub is so fond of Kneecappa that he has even gifted him with his own grot-sized mega armour.
the-waaagh.com, and greenstuff for the grot's arms, legs, rear torso and head. As well as various bits and bobs and wires from the bits box.
I started building him before GW ever released plastic grots. If I were to build another, I'd simply use an extra plastic grot head, instead of making a greenstuff mold of a metal grot noggin.
Ruleswise, he'll count as my Warboss' Attack squig.
I know scratchbuilding and painting his was a lot of work for a simple 15pt upgrade, but the main point was the fun of the build and the silliness of having a grot in mega armour. As a bonus, he neatly explains why a mere "squig" would provide an extra power klaw attack, as well a being able to survive the amount of damage that gets thrown at a megaboss...
It's dark out now, but I should really try to get a size comparison pic with him next to an Ork Boy and a Meganob. He's only half a head taller than a normal Grot.