Profile, Abilities and Weaknesses description from The Transformers G1 series by Marvel Comics.

Profile: Don't be deceived by Tentakil's gentle touch and soothing words -he is undeniably the cruelest, deadliest Seacon. His style is as distinctive as it is lethal.  He showers a potential victim with kindness, offering him help, even complimenting his appearance. And then, once he has gained the confidence of his victim, Tentakil moves in for the kill. In a flash, kindness turns to cruelty. The soft caress of his limbs turns into a deadly, unyielding stranglehold. He seems to take a perverse pleasure in these amiable charades, enjoying them even more than their inevitable, lethal conclusions. As his fellow Seacon, Nautilator, likes to say about him, ''Tentakil can charm the fuel right out of your chassis." And given half a chance, he will.

Abilities: In octopus mode, Tentakil can crush a submarine as if it were a soda can.  Powerful electromagnets embedded within his tentacles enhance his strength to awesome proportions, giving Tentakil the viselike grip that he is infamous for.  Electrically charged feelers on his tentacles' surfaces can short-circuit and stun anything of an electrical nature on contact. While retreating, he can discharge a cloud of viscous black grease to hinder any pursuers. In weapons mode, he turns into twin 50,000 Volt lightning rifles, which can operate on land and sea. He is insulated from any electrical attacks himsetf, so the rifles can't electrocute him underwater. In robot arid octopus modes, he wields dual laser-guided slime blasters, which shoot globs of highly adhesive gelatinous goo. He combines with his fellow Seacons to form the super-robot Piranacon.

Weaknesses: A mysterious short circuit in his wiring often inhibits Tentakil's abilty to transform from one mode to another. This causes him severe problems when he's stuck in robot mode underwater, or octopus mode on land.
In these situations, the modes are poorly suited for the environments. In fact, on land, his octopus mode is more likely to keel over than take a step. 

Bibliography of significant appearances: 
* (Marvel) Transformers #47- All members of the Decepticon Seacon team are seen hunting the pirate treasure off the shores of "Club Con" in this episode.
* (Marvel) Transformers #49- Under the command of (gulp, I can hardly say it) "Commander Ratbat," The Seacons unite into Piranacon.
* (Marvel) Transformers #50 - The Seacons get a very brief cameo appearance in trying to lay a smackdown to a soon to be Underbase powered Starscream.
* a few additional cameo appearances in a couple Marvel UK comics, including UK #268 where the team is (relatively speaking) featured.

Other Appearances: