League of Legends roster! It's the amazing Mercury Hammer or Mercury Cannon, the transforming weapon wielded by the aforementioned Jayce. Jayce is himself a character organized around a special dual-mode weapon kitted out for both ranged and melee carry roles. As a result, he has a broader range of potential builds and a need for a variable playstyle, one that makes full use of his multi-role talents.
When using his weapon as a cannon, Jayce can create fields to accelerate allies and projectiles, deploy area-of-effect attacks, or hasten his attacks. He can then move into melee range and make use of localize area bursts, mana regeneration on his attacks, and increased armor. Moving in and out of range and switching between the roles is most advantageous, as he gains benefits for each switch between modes, meaning that expert Jayce players will need to be quick to adapt to a shifting situation.
[Thanks to Dengar for the tip!]