If Mammon brought up some bad memories, then Verde was in a class of his own in that regard.

After he became a stuntman, but before his career as Skull, The Immortal Stuntman came to fruition, he was kidnapped by some mafioso. They would experiment on him, and once they found out he would come back from dying each time-

He still remembers the faces of the scientists vividly. The calculating gleams, hands shaking in anticipation of new scientific discovery, no matter the costs! What does one life of a measly civilian, a cloud, matter?

It mattered a lot to Skull. He burnt the entire lab down.

Later Skull finds it ironic. After joining the Mafia, he learns that they were Miafioso, that they only reason that they kidnapped him is because of his flames. He finds it ironic because that is what allowed him to escape.

But the scientists, they reminded him greatly of Verde. The same look in his eyes, the same disregard for human life - as long as he could experiment, learn something new; he couldn't care less. The only saving grace for Verde being that he would not needlessly experiment on others; he didn't experiment for the fun of it, didn't torture for fun, but more for the knowledge.

But it is that callousness that sometimes sends Skull into flashbacks.