"Survival of the fittest" doesn't just mean strength or speed - sometimes it's the smartest creature who gets to pass on their genes to the next generation.
See, while Sven and Ollie are charging headlong at the giant flaming dragon, Dave has opted to instead disguise himself as one of its kin - surely it wouldn't attack one of its own, would it? Of course not! That's why he's clever, and that's why he lives long enough to go home and stick it to Lena.
The viking, the dwarf and the man in the lizard suit are all from Lego's series of blind-bagged minifigures. The dragon is from McFarlane Toys, and the flame effect is the same one we've used before.