What about the possibility of explosive propulsion? For example, let's assume that Lavos is either A) not the first of it's kind or B) this is not the first planet Lavos has conquered and destroyed.
If that's true, is it possible that Lavos annhilated another world, and in the end the world more or less "self detonates" (Or, even, Lavos causes it to explode entirely), thereby creating propulsion? It would give some possibility to any heat surrounding Lavos; the force of a super nova would be considered massive, and, if Lavos' shell could sustain it through it, perhaps the heat would also remain constant (I'm not an expert in regards to science, or anything for that matter, so I'm purely guessing)? If it's shell can protect it from such a massive explosion as a planet exploding and giving it the propulsion needed to land on another to continue it's cycle of consumption and reproduction, it would be able to protect it from the impact of landing on the planet.
Also, in regards to PD-1, perhaps it can't create it initially, but almost as soon as it's underground and has tasted and absorbed a bit of the planet's nutrients, it has enough energy to create the pocket dimension? This is assuming Lavos creates it (I can't seem to remember if it was created or simply an occurence or what) and not that it is some kind of alternate phenomenon.
Also, in regards to CyberSarkany's comment, it's also possible that Lavos' impact is exagerated, much like the characters' sprites. Even if Lavos were the equivilant of a 1-pixel or 4-pixel meteor, at the rate of travel, it would still be able to sufficiently create a large crater of impact. The only thing that boggles my mind is how Tyrano Lair got pushed underground instead of being annhilated.
