Gravity Falls - Bill saw his fate at the last minute.

"AXOLOTL MY TIME HAS COME TO BURN I INVOKE THE ANCIENT POWER THAT I MAY RETURN"

Pretty sure it was just XOLOTL, the aztec god of Lightning, death, twins, monsters, misfortune, sickness, and deformities.

Makes more sense than an Axolotl, which is an aquatic creature.