The Deathgrippers were introduced carrying Grimmel's airship to the Warlords' island. Upon reuniting with them, one of the dragons tackled Ragnar the Rock and was called off by Grimmel upon instruction. Later on, when Grimmel met Hiccup at his house, he was threatened by the Dragon Riders and summoned his Deathgrippers to burn down the house with their fiery acid.
When Valka was flying on scouting patrol, two of the Deathgrippers attacked her and Cloudjumper, unsuccessfully attempting to knock her off of the Stormcutter as they were thrown away and called back by Grimmel. The Dragon Riders attempted to capture Grimmel, learning that he controlled the Deathgrippers with their own venom attached through vials in their collars. He ordered them to kill the riders, chasing them out of his base and very nearly killed Hiccup. The Deathgrippers were then attacked by the Rescued Crimson Goregutter who demolished the base and trapped the dragons under debris. With Ruffnut left behind, she was placed in a cage with a Scuttleclaw, of which is predisposed to be fed to the Deathgrippers (to Ruffnut's disgust). Upon supposedly annoying Grimmel into submission, she was set free and given the Scuttleclaw as a means of transportation back to New Berk.
Carrying his airship, they followed Ruffnut to New Berk and revealed themselves when Grimmel captured Toothless and his mate, attaching them to the ship. They carried the airship back to the Warlords' armada, with Berk's dragons in tow. A battle ensued between the Dragon Riders and the armada, and Toothless inadvertently blasted two of the Deathgrippers free of their shackles, leaving two struggling to carry the falling ship. The ship then crashed into the sea, but the Deathgrippers survived and chased after Hiccup and Toothless. Later on in the battle, as Toothless and Hiccup chase Grimmel and the drugged Light Fury, the two Deathgrippers attempted to attack them, but they were defeated when one was knocked into a hill and the other was crushed by a rockslide caused by Toothless. The four remaining Deathgrippers continued to harass the duo and tried to keep them away from their master. As they formed a tight ring around Toothless, he summoned lightning in his Alpha state, electrocuting all four Deathgrippers and sending them plummeting into the sea, leaving their final fate unknown.
Your Grimmel poison antidote was a success! I think. I assume you hit this guy with your antidote? This Deathgripper landed here a little bit ago, disoriented. He won't let anyone get close to him. So, not great. He's not attacking us so that's definitely an improvement. Maybe he'll let you approach him. Thor knows that he won't get comfortable with anyone else!
At some point during Berk's move to New Berk, the Warlords set up camp on Glacier Island. The Riders attempt to attack the camp, but Grimmel appears and captures Cloudjumper with his Deathgripper venom. Later, the Riders concoct a possible antidote to Deathgripper venom and attempt to save Cloudjumper. Astrid and Stormfly go head first into battle with a mind-controlled Cloudjumper and two of Grimmel's Deathgrippers. Cloudjumper shoots Stormfly and Astrid out of the sky. The School of Dragons player tries to sneak up on Cloudjumper and tosses the antidote, only to miss and get some on one of Grimmel's Deathgrippers. The mission to free Cloudjumper failed. The Riders return to New Berk. However, Hiccup informs the School of Dragons player to visit Fishlegs. The player meets Fishlegs trying to calm down a male Deathgripper who is confused and anxious after being released from the thrall of its own venom. After the player is able to approach and calm the Deathgripper, he stays with the player on New Berk.
Grimmel's Deathgrippers are presumably representative of their species. They all have a base color of blood red, with thick black marking on the body and limbs. They also have a pair of white tusks, and plating down their backs and tails. Every one of them also possesses a venomous stinger on the end of their tails.
All six Deathgrippers wear collars equipped with vials of their own venom that Grimmel uses to control them.
One of the Deathgrippers also appears to have a scarred eye.
Deathgrippers are described as "vicious dragon killers" by Dean DeBlois which would apply to Grimmel's as well, making them handy 'tools' for the hunter.
Abilities and Skills
My Deathgrippers' bite is worse than their bark.[src]
Strength and Stamina: Four of the Deathgrippers are able to carry Grimmel's airship over long distances without any signs of struggle. They are also strong enough to temporarily stun the larger Cloudjumper and can survive a wreckage of rocks that fell upon them.
Speed and Agility: The Deathgrippers are able to move swiftly on land and in the air. They can fly fast enough to catch up to Toothless.
Senses: The Deathgrippers are able to smell and hear the Dragon Riders approaching in the middle of the night.
Combustive Acid Breath: Unlike other dragons who normally spit fire in some capacity. Death Grippers spit an incredibly volatile form of corrosive agent which burns and sears anything it comes across. Said solvent also seems to catch fire when exposed to open air, setting most anything it touches ablaze in seconds.
Retractable Stingers: The tails of the Deathgripper possesses a hidden, razor pointed stinger which it hides in a flower like bulb at the tip of it's prehensile appendage.
Psycho-Active Venom: Deathgrippers release a form of neurotoxin from the point of their tail stingers which plays havoc both on the mind and the nervous system. The toxin can have numerous properties depending on how its prepared, features which Grimmel uses to expert effect in his dragon hunting profession.
The first is a Neurocognitive Deficiency where those affected are left in a state of muscle relaxation, drowsiness and disabled motor function.
The secondary effect is a form of mind control which Grimmel found has a powerful will numbing effect he makes practice of through a direct cranial injection harness fitted both around his prey and his own dragons. The strength of which is so potent that his control cannot be undone even by an Alpha Dragon.
They serve me, and only me. Allow me to demonstrate.[src]
— Grimmel to Hiccup, before ordering his Deathgrippers to kill the Dragon Riders
Grimmel has subjected six Deathgrippers to his command by using their own venom against them. He did this by sticking vials of their venom into their heads through a collar that each one wears, drugging them into absolute obedience.
The Deathgripper with the damaged eye seems to be a nod and a resemblance to One Eye from the books.