Like a snake swallowing his own tail, the memories and vices and errors of Sir Pentious's life carry over through his death. A character study.
In life he sought, strived to live up to the standard set by his father. Always he was shunned, set aside, in some way insufficient. He saw himself surpassed and outclassed by rivals and opponents; vowed to overcome them only to be trounced again despite his best efforts.
In death, he resents the successive rejections by the overlord class he seeks to join; the foes who consistently anticipate his plans, demolish his inventions, yet do not grant him the recognition he craves.
He has a legion of unwavering minions but, well...
Manufactured loyalty cannot replace some things (like lost kin).
This turned out sadder than I intended it to - somebody give the Doofenshmirtz noodle a hug.
I've jumped on the bandwagon for the theory that Sir Pentious had a son, who became estranged from his father at some point, and that the snake is still kinda hoping to find and reconcile with his kid in the afterlife.