The fifth episode of Invincible season 1 introduced several new supervillains, including a savage alien mercenary known as Battle Beast. Beyond being one of the most dangerous beings in the universe, Battle Beast is also an homage to a relatively obscure action figure line of the 1980s.
The episode "That Actually Hurt" found newbie superhero Mark Grayson (aka the hero Invincible) entering into an unlikely alliance with a low-level supervillain called Titan to bring down the gang leader Machine Head, who had blackmailed Titan into working for him after Titan borrowed money to pay for his daughter's surgery. Titan and Invincible found themselves outgunned, as the cyborg crime boss had predicted Titan's betrayal and hired some new bodyguards capable of taking them out. Among them was a being known as Battle Beast, who was able to defeat Invincible, Titan, Robot, and the rest of the Guardians of the Globe who faced him. The only thing that saved the heroes was the fact that Battle Beast had apparently come to Earth seeking a worthy test of his warrior skills. Having found the most powerful superheroes on the planet to be unworthy of his time, Battle Beast abandoned the fight to seek new challengers elsewhere.
Battle Beast's name and appearance seem to be a reference to the Battle Beasts toy line. First released in Japan in 1986, Battle Beasts was a spin-off series of Transformers and was originally marketed as BeastFormers despite the characters not changing shape. The Battle Beasts were a race of andromorphic animal-men from Planet Beast, who allied themselves with the Autobots and Decepticons in a bid to settle their own civil war. Unlike the technology-based Transformers, the Battle Beasts drew strength from primal energies, with each warrior calling upon the elemental powers of Wood, Water or Fire. While the connection to the Transformers was removed when the toys were repackaged for sale outside of Japan by Hasbro, this rock-paper-scissors mechanic for fights between Battle Beasts remained.
Battle Beasts was not as successful in the United States as it was in Japan, with most of the fourth and final wave of Shadow Warrior Battle Beasts never seeing a release in the USA or Europe. There were several efforts to revive the line in the early 21st century, but none of them saw much success beyond a short-lived comic book published by IDW. Amusingly, it is far easier to find images of Battle Beast from the Invincible comics online today than it is to find pictures of Pirate Lion (aka White Leo) - the lion-headed leader of the Autobot faction of Battle Beasts, whom Battle Beast seems to be modeled upon.
The nod to Battle Beasts is one of many Easter eggs worked into the reality of Invincible, for seemingly no other reason than it amused Robert Kirtman to do so. The same episode which introduced Battle Beast also contained an amusing Easter egg regarding actor Reginald Vel Johnson, who provided the voice for Mark Grayson's school principal, Mr. Winslow. The high school in the original Invincible comics was named in Vel Johnson's honor and the principal's name was a nod to Vel Johnson's role as police officer Carl Winslow on the show Family Matters.