No known relatives
The 50 Year Behemoth is a gigantic Behemoth that only appears once every 50 years.
The 50 Year Behemoth's first recorded appearance was in 3000 BC, and it has presumably appeared once every fifty years ever since.
The Behemoth appeared in 1960, but was defeated.
Fifty years later, the 50 Year Behemoth appears again in the ocean, and begins a rampage towards the shore.
However, You arrive in a helicopter and, despite the Behemoth's attempts to swat You away, You fire several fission blasts into the Behemoth's skull before it reaches the shore, causing it to phase-shift back into a dormant state.
The 50 Year Behemoth appears once every 50 years at any random location for reasons unknown and will then devastate everything in its path.
The 50 Year Behemoth is physically identical to an ordinary Behemoth, except it is ten times the size of a typical one.
The 50 Year Behemoth possesses colossal strength.
The 50 Year Behemoth's single weakness is a small exothermic cluster in its skull. If this cluster is hit with a nuclear fission reaction, the 50 Year Behemoth will phase-shift back into a dormant state.