The Sentinels in how we've seen it is no longer considered canon, as there were too many Sentinels publications that went their own way(in other words, the movie is different from the comics, which are different from the novels until way later, and then the movie isn't even really episodes 1, 2, and 3 in order). The show/novels/comics/RPG had gone in so many different directions that HG decided to wipe the slate clean and "pick and choose" what they liked.
Originally Posted by BigEclipse
The concept isn't totally dead as some events were acknowledged in the Prelude to the Shadow Chronicles comic that was released late last year, but if it was the same as what was seen before is anyone's guess.
With multiple forms of Grim, its clear he's a dragon ball z character in his powered down state. DONT GET HIM ANGRY!
-MrAngryFace, GA Forums, Thread "So, what exactly is the Grimace?"
"You can't end a good party without someone on the floor." -Yusuke Urameshi