The Brawler archetype Constructed Pugilist grants you a prosthetic arm right off the bat that you can modify yourself through class features and crafting feats. One such class feature lets you use it like a grappling hook against enemies.
Constructed Limb (Ex) A constructed pugilist begins play with a special prosthetic limb built for fighting and typically made of iron, steel, stone, or wood, with the corresponding hardness and hit points. She treats attacks with this limb as unarmed strikes that gain all the benefits of the brawler’s unarmed strike class feature. She treats the limb as a light weapon and is proficient with it. Removing or reattaching the constructed limb takes 10 minutes.
The constructed pugilist can improve her constructed limb as if it were a normal melee weapon. For the purpose of rebuilding the limb as a masterwork weapon, rebuilding the limb out of a special material, or adding certain magical special abilities to it, the limb counts as a one-handed melee weapon that costs 60 gp and weighs 6 pounds—though it is specially fitted to the constructed pugilist and can’t be resold or used by anyone else. A constructed limb can benefit from either its own enhancement bonus and special abilities or those granted by an amulet of mighty fists, but if it would benefit from both simultaneously, it benefits only from the source with the higher effective enhancement bonus (the limb benefits from its own abilities in the case of a tie).
It calls out that the arm is treated as a light weapon and an unarmed strike for the purpose of combat.
Grapnel Arm: The constructed pugilist can fire a grappling hook built into her prosthesis. The grappling hook is attached to a 40-foot-long fine chain affixed to the limb. The constructed pugilist can attack with the grappling hook as a standard action, making a ranged touch attack against the target. The grappling hook can’t be used as part of a full attack. On a successful hit, the grappling hook deals no damage, but it functions as though it had the grapple weapon special feature, except it requires only a hit (not a critical hit) and the grapple ends if the constructed pugilist moves more than 40 feet away from the grappled creature. The constructed limb can’t be used to make melee attacks until the grappling hook has been reloaded (a standard action).
Using the grapnel arm is done as a ranged touch attack. Spellstrike calls for a melee attack to be made in place of the normal melee touch attack for delivering the spell. The archetype Eldritch Archer has a Ranged Spellstrike to be used through an actual ranged weapon. I do remember seeing somewhere that the Magus using the Prehensile Hair hex or multiclassing with a Witch using the White Haired Witch archetype was able to grapple with the hair and use spellstrike without need for another attack, but I'm not sure how official the ruling is on that. Would using the Grapnel Arm ability work in conjunction with Spellstrike? Would I have to use the spell before an attack or could it be done after it's already attached?