The Hero Splatling Replica is unlocked for multiplayer use by beating the single-player campaign using the weapon.
The Hero Splatling is a metallic silver weapon, which like other Splatling type weapons, must be charged up to use. When the charge button is released, it rapidly unleashes a powerful barrage of ink over a long range. It comes with the Sprinkler as it's sub weapon, and the Sting Ray as it's special.
In Hero Mode, the Hero Splatling can be upgraded to have a longer range and a quicker charge time.