From: Black Friday
It's wacky buddy movie time as Blackarachnia forces Optimus Prime and Grimlock to team up together. Grimlock enjoys putting the scare into the "puny humans" until Optimus convinces him to transform to robot mode.
The transform is mostly an excuse to post a bit of Grimlock, and a funny exchange between the two characters. This episode was basically a David Kaye festival, as he voices both Optimus Prime and Grimlock.
Meanwhile, Snarl and Swoop still haven't talked.
Note that while Optimus Prime and Grimlock's toys are both Voyager sized, Optimus is actually slightly taller than Grimlock.