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 far less useful than the Lava Gun and differs in function completely. It fires out several meteor chunks which have a much lower rate of fire, and cannot easily hit multiple enemies at once. It is slightly better against larger enemies, but is still heavily outclassed in this regard. The Lava and Meteor Gun have two weapon modifications: the acid mod which damages enemies over time and the lock-on mod. The lock-on mod provides little use to the player, while the acid mod improves damage and suits the weapons' use against weaker enemies. However, as the Meteor Gun is far less useful than the Lava Gun, players should prioritise purchasing mods for other weapons instead, as Lava Gun mods will only briefly be useful.
The Liquid Nitrogen Gun upgrade in Up Your Arsenal, however, is equally as useful as the Lava Gun. This upgrade functions identically, 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.