User blog comment:Lord Loss/Monster Hunter Theory... Blog/@comment-15400750-20130820160324/@comment-5963861-20130820233656

An Agnaktor's body is capable of secreting a nonflamable fluid between the openings of its scales, thus making them able to swim in lava for long periods of time. As for Rathalos I'd imagine it's skin is tough enough to resist lava if it just steps in it, not splashing around in it like Agnaktor does. On the subject of Deviljho its pretty much just game mechanics like whenever a Rajang walks in lava in unite/frontier as they're skin has no special adaptations to move around in lava.