The Phantom Blot's appearance clearly invokes that of a medieval executioner which makes sense on two fronts:
The first is that Blot's end goal appears to be the destruction, or "death", of Magica and all magic.
The second is a bit more WMG but Magica said her encounters with Blot began decades before meeting the McDuck-Duck family a rivalry that goes back centuries. Magica is clearly a case of Really 700 Years Old so its possible, nay probable, that the Blot is actually from the Middle Ages and never updated his outfit.
The fact that the ATM only gave Gladstone 20 dollars means he couldn't buy the meal which cost 34 dollars (and he definitely wouldn't get a discount either). Another sign his good luck was gone.
Gladstone being able to get $20 on the other hand when nothing is going right for him means he was at least smart enough to open a bank account, but likely forgot he even had one.
Gladstone's luck in this episode isn't outright bad luck, but mostly just regular "luck"; nothing that happens to him is as ridiculously unlikely as everything he experiences with his regular good luck (seriously, what are the odds that he's never had to walk anywhere in his life because of freak gusts of wind?), but basically amounts to him having to deal with regular issues and finding himself unable to handle it.
Why would F.O.W.L. allow the Phantom Blot to join their ranks despite his Adaptational Heroism? Because as Bradford cites in Let's Get Dangerous, Magica's apocalyptic return was another reason as to why Scrooge and his family needed to be stopped. So hiring a magic hunter who's driven to taking down supernatural threats like Magica would be a great benefit to Bradford's Pragmatic Villainy themed agenda.
If the girls had chosen to go on the adventure to the goat's realm with Scrooge and the boys, they probably would have been trapped there for a long time (if not forever) after the Phantom Blot drained the magic from the portal.
The implication that the Phantom Blot used to be an innocent villager, and his current form probably came from all the magic he's been absorbing for years, corrupting him.
This episode clearly demonstrates that Gladstone would not last two days on his own without his magic luck, and he'd definitely die from his own stupidity and clumsiness. Case in point, he got hold of the amulet, and shot it without checking it wasn't pointing towards himself. If under the same circumstances it were something like a firearm, Gladstone would've done himself in.
The Phantom Blot doesn't realize threatening to kill Lena will not break Magica because she doesn't care about her niece, but would the Blot have stopped if he had known that? Not likely. He'd still attempt to kill Lena because she is still a DeSpell and wielding the very magic that killed his family and destroyed his home. For him, the only good DeSpell is a dead one.
And even if he had gotten his revenge, he'd still continue on to destroy any magic, uncaring what consequences his actions may cause.
Of course, just how many people has Magica hurt, and how many people want revenge against the DeSpells? Not a lot of people are going to be forgiving towards Lena because her family has caused pain to the world for generations.
Magica got her magic staff back until Lena sent it into the swamp nearby instead of you know, taking it from her. Magica’s going to find her staff again sooner or later, as she herself saw where her staff dropped. It’s only a matter of time before Magica is threatens the McDucks again.
Magica reveals that she enslaved an innocent village, robbed them of their riches and then killed everyone when she got bored with them. Thinking back to her return in "The Day of the Ducks", Duckburg was very lucky that the Duck family was able to stop her before they ended up like the Blot's unfortunate village.
