(Top-Notch Comics 009, 1940)

The Skull is the recurring foe of the Golden Age Black Hood, and as is common for such characters he is a kind of generalist super-villain willing to dabble in everything from theft to kidnapping to espionage to murder as circumstances dictate. He even indulges in a little housebreaking on occasion, and it is while doing so that he is interrupted by police officer Kip Burland, who he frames for the crime and then eventually attempts to have murdered when he refuses to give up on proving himself innocent.
This of course is the origin of the Black Hood, as Burland recovers and trains under the tutelage of one of the Skulls other victims. Accidentally creating your own nemesis is one of the occupational hazards of being a successful super criminal, after all, and the Skull is so successful as he kind of did it twice, as Kip Burland's mentor is a different lawman who the Skull framed and ruined who swore revenge on him but then took too long preparing and had to be content with weaponizing another to do the deed.
By the time that Kip Burland is prepared to go into action as the Black Hood, the Skull has devised the first of what I now recognize as his signature: an overcomplicated scheme. Specifically, he has targeted the debut/masquerade ball being held for wealthy socialite Barbara Sutton, and has not only informed all of the guests that they must show up in their best jewelry so that he can steal it but has also announced his plans in the papers. I think that the intent is to ensure compliance through fear, but it really seems like he's just introducing ways that his scheme can go wrong.
The Skull's instructions are clear: he will steal the jewels off of the guests during the party and they are to keep quiet about it. None of them manage this, and each victim ends up being killed via a blowgun dart tipped with a poison that turns the human head all green and corpsey. Plus - and this is hard to see but trust me - the dart leaves a little skull-shaped mark at the point of contact.
The Black Hood eventually works out how the Skull is doing all this: he has disguised himself as hostess Mrs Sutton and has been shooting the darts out of a blowgun shaped like a cigarette holder. One dunk in an oversized decorative vase later, the case is solved!
(also please note that the Black Hood is in attendance in costume as himself. It still counts even if this is his first public appearance in costume)
After the Black Hood turns the Skull in to the police at the end of his first costumed adventure, his ally the Hermit predicts that they will be unable to hold him, and what do you know but he's right. The Skull dramatically breaks jail and immediately puts another overly complicated scheme into action. Major Quentin Duff has invented the unspecified-but-presumably-valuable Iota Ray, and the Skull wants it, but is not prepared to do anything so simple as to steal the plans. Instead, he implements a simple three-part plan:
Step One: ambush Major Duff at his house and murder him just after he hands the Iota Ray plans over to Mrs Duff for safekeeping.
Step Two: While Mrs Duff and Barbara Sutton are taking the plans from Washington DC via train, kidnap Duff and gaslight Sutton into believing that she was never there. This requires at least a half-dozen confederates as well as an appearance by the Skull as a Dr van Luks, a backward name so annoying that I audibly groaned when I worked it out.
Step Three: Once the plan falls apart, just try to murder everyone and take the plans off of Mrs Duff's body. Please note that this step was an option from the start, and that the theft could have been committed using the Major's gruesome murder as cover.
As 1940 draws to a close, the Skull is left shaking his fist after a speeding train as the Black Hood escapes with the plans. We will see him again in 1941!
SKULL SCORE: A very generous 2/5, considering that this particular Skull isn't actually missing any facial features. The combination of his emaciated face, sunken eyes and perpetual rictus goes a long way nonetheless. Plus he's green.