As
The Stoopid Unikorn
already said, the spear would be blockable like Isabelle's fishing rod, which I believe is true to the source material as, at least in the old arcades, it could be blocked.
The way I see it working would be that it would have a range between a Hookshot grab and Isabelle's fishing rod and would grab an unblocking character if it connects anywhere in that range. If the move miss/extends past the grabbing range, it become a mild projectile with small damage and flinching (it can be reflected/pocketed at any range and loses the grab property after doing so). It'd be a fairly slow attack to perform, roughly the rate of a Hadouken, but travels fairly quickly. When grabbed, the opponent will be brought over to Scorpion with a brief amount stun, that is scaled around how much damage the target has, which amounts to about as much as a buried opponent would get. This would allow Scorpion to perform a quick action of his choosing (the Spear's fire rate would be too slow to repetitively use) much like it has behaved historically.
I think that would keep it unique, true to its source material and not broken.