Alchemist had brought out 11 skeletons, but he can only control 10 skeletons per level. He was testing what would happen to any extras if his level went below what he could control.
The answer is that the oldest skeletons go feral, which is distinctly not the answer that he was hoping to get. It means that, should he transmigrate or have something else happen to him, the great big army of undead that he made is now wild and uncontrolled and ready to go and murder everything nearby that isn't also undead.
So that's one plan of his that just isn't going to work out. It's not a total wash, he can still do a bit with it, but it's just never going to end up like he hoped it would.
Older D&D rules give more powerful undead the option of controlling weaker undead. This is usually 2HD per HD of their own. So a 2HD ghoul could control 4 1 HD skeletons.
So, AL controls the most powerful undead, and they rank down controlling less powerful undead underneath them, expanding the size of his army through indirect control. It won't be as tight or responsive, because commands would be repeated, but he would be in control.
But, yes, the uncontrolled undead immediately go feral. This is the exact same thing as controlling undead at your cap and then getting the newest and latest model, the uncontrolled ones you let loose immediately return to their normal behavior.
Also note, Undead can also be created by Curses, which does not involve necromancy, and doesn't have to be evil. D&D did allow good undead at one point (archliches), but has largely backtracked on that. Paizo, of course, has the standard rule that true undead are ALL Evil, no exceptions. There can be good restless spirits, but they aren't Undead if that is the case.
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Almost all alien races in DC have some sort of power or ability that is superior to that of Humans. No superpowers? They gave a power ring to a Daxamite, who are a branch of Kryptonians! Kilowog is superstrong and durable. Arisia regenerated from death and can live for centuries. There are intelligent viruses and plants and whatnot.
Plenty of Green Lanterns have 'super powers' by human standards, even if its only enhanced physical ability in some fashion. They've recruited mentalists, super stealthers, super agile chipmunks, and tons of different things. The most common is probably they are significantly smarter on average than humans are, like Sinestro's people.
But smarts aren't what drives a Green Lantern ring.
The biggest thing for the Humans is that they have high Willpower by Corps ratings, with Hal Jordan topping the scale for everyone. Humans who qualify for Rings are almost always incredibly suited for them.