Animal + Element = three and a half pages filled.
All flame snakes share the fire subtype, scent, and the ability to deal extra fire damage with their touch. They come in three sizes.
Flame Snake, Minor
These small-sized magical beasts only have one RHD. They receive a large dexterity bonus, a little strength, and a smaller intelligence penalty (only -4) than most beasts of this level would. Their sole natural attack is a bite that deals 1d4 damage (plus 1d6 fire) and injects a strength-damaging poison that also deals gradual fire damage for a minute or so.
Additionally, once per day minor flame snakes can cast CL3 Burning Hands. 3d4 fire damage is just enough to consistently knock out first-level goblins and kobolds, but rapidly becomes useless at higher levels.
While a fire immunity is never bad, and the stats are reasonably well-suited to a rogue, the lack of limbs is a large burden that remains as the bonuses fade. That said, it's just barely enough for a +0.
Flame Snake, Lesser
The medium size, tail sting, fast healing, uncanny dodge, and ability to spit magma simply don't make up for eight magical beast HD, not even when you add in the slightly bigger overall numbers. -0 LA.
Flame Snake, Greater
With seventeen RHD, this snake has one niche and one niche only: tank a few attacks, explode in someone's face, and reroll as something better. -0 LA.