Shockwave

Shockwave was a strange Decepticon who randomly decided to camp out on Earth for thousands of years for no reason. He apparently lived on Earth for the entire time that Megatron was frozen there, but didn't get him out. He is also fused into a weird giant drill thing, or the drill is his pet, we don't really know. Either way, he could've used that to break through Hoover Dam and snatch the Allspark but he didn't do that either.

Nope, he just sat there, and only showed his ugly, weird, one-eyed face during the Third Decepticon Incursion for no particular reason other than to sell toys to fight Optimus Prime. He stole a weird nuclear thing from the Autobots and then ran away to a city where he ordered loads of Decepticons around, including Barricade, but his drill pet was decapitated and he got his eye tore out by Prime before being minced to death, and his giant gun was used to shoot at Sentinel Prime for a bit. How nice.