In Going Commando, the Lava Gun can be upgraded to the Meteor Gun, which fires meteors instead. In Up Your Arsenal, the Lava Gun instead upgrades to the Liquid Nitrogen Gun, which fires a continuous stream of liquid nitrogen that freezes enemies.
The Lava Gun was available from a vendor for 25,000 bolts upon reaching Tabora. With use, it could be upgraded to the fundamentally different Meteor Gun. In challenge mode, the Meteor Gun could be upgraded to the Mega Meteor Gun for 200,000 bolts, and in turn to the Ultra Meteor Gun.
Up Your Arsenal
The Lava Gun could be purchased from Slim Cognito on Aquatos for 40,000 bolts, or obtained for free if the player had a Going Commando save file. Unlike its previous appearance, the Lava Gun upgraded to the Liquid Nitrogen Gun with use, which had much the same functionality. Upon reaching challenge mode, the Liquid Nitrogen Gun could be upgraded to the Mega Liquid Nitrogen Gun from any Gadgetron vendor for 260,000 bolts.
The Lava Gun is a long rifle covered in different shades of red. It features a left-hand grip, and a canister of lava preceding a slimmer nozzle. It spewed out an orange stream of lava a short distance in front of it.
The Meteor Gun and the Liquid Nitrogen Gun upgrades both share largely the same appearance. The weapon is longer with a much larger canister that takes up most space, with only a left-hand grip, a few tubes and now much larger nozzle. The Liquid Nitrogen Gun only differs in color, being completely blue rather than orange and red.
The Lava Gun fires a stream of lava which burns enemies, dealing decent damage. The physics of the weapon make its stream correspond to Ratchet's movement, allowing him to spread the stream out further. It is extremely effective against large mobs of smaller enemies, as it can hit many at once in a close range and has plenty of ammunition. While best suited against mobs of smaller enemies, it is still useful against larger enemies, though it does not damage them as quickly as many other weapons do.
The Meteor Gun upgrade in Going Commando is ineffective and unreliable on its own due to its short range and random spread. However, both problems can be mitigated by purchasing the lock-on mod, which turns the Meteor Gun into an accurate, medium range weapon akin to a much more powerful version of the Heavy Lancer. As the Meteor Gun's damage output was balanced with respects to its range and spread (200 shots from the Meteor Gun deals roughly 80% of the Mutant Protopet's health in damage), it becomes extremely powerful compared to other weapons once lock-on is available. Due to its high ammo count, the Meteor Gun is also extremely cost-effective, making it arguably the most powerful and versatile weapon until the player can afford the RYNO II.
The Liquid Nitrogen Gun upgrade in Up Your Arsenal functions identically to the Lava Gun, with the only difference being a freezing animation of enemies being killed by the weapon. Therefore, the Liquid Nitrogen Gun remains very useful against large mobs of small enemies, though it is still outclassed later by weapons such as the Plasma Coil and the Qwack-O-Ray.