Need confirmation on untamed.
Also I suggest an 'Ambassador' type weapon (crits on headshot).
And for a novel weapon, how about a reverse shockwave which works similarly to the hookshot. Once a projectile is fired the boss cannot fire another one until it hits something. Alt fire is normal hookshot. It shouldn't be able to pull people in the tank turret.
The projectile should be easily visible but not huge. Something on the lines of the size of samus' normal shots. Projectile speed should be somewhat slower than samus' normal shots as well.
This would be balanced due to the one-projectile-at-a-time which only allows netting of one person at a time. Accuracy is needed for kills. Close-range hits also shouldn't kill as the acceleration wouldn't be high enough for fall damage to take over.