Throughout the series, Demona has made use of several differing firearms when battling her enemies.
Demona used a poisoned tipped dart fired from a tranquilizer gun in an attempt on Elisa's life. Later on, she used a large particle beam blaster to shoot, and wound Goliath... perhaps mortally had Hudson not managed to keep him alive until sunrise.
As she battled Hudson, Demona lost her temper and, rather than fire her weapon, attempted to bludgeon Hudson to death with it instead. The next night, Hudson took the gun from her (she didn't resist) and he must have disposed of it.
Demona brought a high-powered particle beam cannon into battle, but was quickly disarmed by Brooklyn. But she got a hold of it again, and shot Coldstone with it (a blast meant for Goliath), knocking him into the frozen Hudson River. She lost the weapon again when Xanatos grabbed her as he rocketed away from the battle.
Demona used a new particle beam blaster against the gargoyles-turned-humans. But, she was disarmed in battle, and the gargoyle-turned Elisa used the weapon against Demona.
Demona made use of both a mace, as well as a lighter particle beam cannon when she was massacring humans that she turned to stone. She even used her cannon to blast the arms off one of them; the results come sunrise are unknown to us.
Demona threatened Elisa with a bazooka at Belvedere Castle, calling her stupid for showing up unarmed. However, Macbeth goaded Demona into fighting Elisa hand-to-hand, and Demona tossed the bazooka to the floor.
After the battle, Demona and Macbeth fled, Coldstone went into self-imposed exile, and Elisa took a nap next to the stone gargoyles. The bazooka was, presumably left lying on the floor of Belvedere Castle out in the open. Whoops.
"Avalon Part Two" & "Part Three"
Under the control of the Weird Sisters, Demona was armed with a particle beam cannon, which she used to wound Ophelia, and to attack the Avalon Clan. But, when Elisa appeared, Demona threw down her weapon and attacked her. Princess Katharine picked up the weapon and used it to end the battle.
Demona used another particle beam cannon while battling Macbeth. She lost it in the battle when Macbeth shot at her in the ballroom. She then picked up Macbeth's own particle beam rifle before being shot by Elisa with one of Macbeth's lightning guns.
"Hunter's Moon Part One", "Two", & "Three"
When Demona battle the Trio at one of Xanatos's warehouses, she was armed with a medium-sized particle beam cannon. She kept them at bay, hiding behind a car, until she increased the power setting to maximum and blew up the car with one shot. She was disarmed by Brooklyn, and the gun went off starting a fire and subsequently an explosion.
Finally, she was armed with a much smaller particle beam cannon, which she used to stun Brooklyn before attempting to wipe out humanity.