When attacking, use Basilosaurus whales, they cannot be grabbed, be aware that once low health, the squid will flee and emit ink, and debuff you by making all nearby creatures aggro you. I almost lost a 265 basilosaurus to 4 dunkleos and 10 megalos that boxes me into a star formation.
Grabby Arms has many arms to grab you with. If you don't have a mount because Grabby Arms has already killed it it will grab you and begin shredding you with its spikey tentacles. If you have a grappling hook you can grab a nearby wall or the ocean floor and pull yourself away. This thing will break primitive scuba gear like a thatch dinosaur gate. Put your riot or flak gear back on before trying to make your escape. Your flippers are broken already.