Arblus is one of the only survivors of Unicron's attack on the robotic planet Lithone at the very beginning of the film. Unfortunately for him and his friend Kranix, the planet they landed on after escaping their doomed homeworld was that of "the savage Sharkticons and their cruel masters, the Quintessons."
Who are the Quintessons? Well, they're so utterly heinous that there'd be too many angry vulgarities needed to properly describe them and how vile they are, but suffice it to say they're freaky aliens who capture people and put them on trial for... some reason.
As Hot Rod and Kup are captured by some Quintesson guards after fending off a variety of awesome-looking robotic sea monsters, they're taken into a courtroom with a big deep pool in the center filled with mechanical sharklike creatures we'll later learn are called Sharkticons.
Apparently for fear of interrupting the proceedings, our heroes' captors hold on off on stuffing them into their prison cells until after the sentence has been passed. As Arblus stands on a sort of plank extended out over the pool, a Quintesson with a head that's ribbed for her pleasure, apparently playing the role of prosecutor, asks a Quintesson with five faces, who is apparently playing judge, "Has the Imperial Magistrate reached a verdict?"
The Magistrate's... let's say "happy" face replies in the affirmative and, asked for clarification, his head rotates around to a vaguely skull-like face and declares, "Innocent."
Now in most justice systems, this means Arblus would be let go, but Quintessons either do everything bass-ackwards, or they just like screwing with people for a laugh, because despite the verdict of innocence, rather than ordering Arblus' immediate release... the Quintesson prosecutor orders his release into the Sharkticon pool!
"Feed him to the Sharkticons!"
And with that, another Quintesson flicks a switch and the plank thing, which it turns out is hinged, tilts down, dropping poor Arblus into the water. The Sharkticons immediately set upon him and begin eating him.
"We need a new travel agent," a thoroughly depressed Hot Rod quips in an attempt to lighten the mood (although it just makes him look kinda callous).