Haven't worked enough with Cave Johnson, so I did a little break and made one. I'd say 15 minutes? While lemons would be a funny cutie mark, that isn't his 'special talent'. Tossed between the original Aperture Science Laboratories logo or a shower curtain. (I know too much about this game X3)

I think I could do these for $5-$10 commissions if anyone wants to get pony'd!

Cave Johnson © Valve
My Little Pony Friendship is Magic © Hasbro