A megolamaniac is someone who has delusions of grandeur and power, so the simile is saying that the person's demands become more and more unhinged and unreasonable.
Consider the statement "It seems like he's just really charismatic, until his demands become gradually more unhinged". Is the statement "It seems like he's just really charismatic, until his demands become gradually like a megolamaniac's." false? Yes/no/unknown