I just wanted to remind you all that lava doesn't seem to affect most algebraliens but fire does. X could go through lava just fine yet was visibly hurt from being set on fire. Four stood on lava like Jesus stood on water and was fine, but got hurt when Firey Jr. set him on fire from the inside by setting Spongy on fire from the inside. I think this is very important to remember as it seems to be intentional since it happened to both X and Four.
Edit: this also means that they are not heat-proof or at least not completely heat-proof because the reason lava and fire hurt is because they're both high temperature.
Btw fire is hotter than lava, but magma that's closer to the Earth's core is definitely hotter than fire. And X went very down (but idk how down) into the Earth.
