When I was using an AI image generator to generate an image of Armadon, this is what I stated so that I could get as close a result as I could to Armadon's look.
A brown, bipedal ornithischian (a hadrosaur) with the head of a Centrosaurus (skull and horn), the frill of a Chasmosaurus, the back armor of a Gastonia or Polacanthus, the tail club of an Ankylosaurus with the thagomizer of a Stegosaurus.
Although the Polacanthus/Gastonia spines aren't as prominent as the spines on his official model, but I would argue that Kentrosaurus spikes are a bit too far to the back of the hips when they're up in the upper back of Armadon's armor.

Best way to describe Armadon is that he's a biped chasmosaurus with ankylosaurus armour and kentrosaurus spines
(A species of stegosaur which had back spines forming into the thagomizer from the backside to the tail, and also had spiked shoulders)

FINALLY THE ARCADE ONES ARE BEING RIPPED!