The Gun that can kill the past

{u}{b}{r}{t}; Search your library for a Legendary Enchantment card and put it in your hand.

When a Past card leaves the battlefield, target player who controls a gungeoneer card takes control of this artifact until end of turn untap it.
{t}; Add three mana of any color, draw two cards and gain ten life. Activate only if you control a Past card and if a Gungeoneer card left the battlefield this turn.
{t}; Add three mana of any color, draw two cards and gain ten life. Activate only if you control a Gun