Here are the designs of the Belshazzars nicknamed Hell Bells because of their bell shaped heads and holes on their bodies (also they ring when they active or move around but its usually muffled from the heavy walking)
These guardians were made for the four kings of Hell during the war against the angels. They have indestructible metal that physical or special weapons cannot pierce thru them (perfect for the arrows and swords the angels used during that time) Because of this unique army of titans, the kings were able to win the war and claim more of the land of mortals (Earth dimension) They are 7'2 feet tall and weight 3 tons. They have a a skull like head with 4 sharp canine teeth in the end and can open their mouth 12 inches wide.
It has been 100,000 since the OWW and the Belshazzars have advanced to newer models in every generation and has better tech than their ancestors. Not only for the kings to use but also any demon in the underworld ( only high class demons can access them but lesser demons can just steal them too so π€·ββοΈ) Btw, if you haven't noticed already, Bean has the New Generation Hell Bell! Neat huh~
(Will design the New Gen Hell Bell later)