Ok, so original plots are possible, which I would HOPE is the case, considering the number of B and C-list characters walking around that could use the spotlight now and then.
This week, it's Edna Krabappel. She gets fired after Bart secretly has her boozed up during school hours. Mild comedy ensues, but nothing mind-blowing. It was a decent episode and all, but I seriously can't believe they didn't acknowledge Edna's past with Skinner AT ALL, considering how much of a focus that was for the longest time.
Skinner's all-too-brief screen time makes this one good. He's quietly become one of the series's most reliable characters.
Actually, not an original plot at all. This was a retread of "Sweet Seymour Skinner's Baadasssss Song," where Bart's hijinks get Skinner fired, and Bart tries to help him turn his life around. In fact, it's a retread right down to the fact that each teacher gets their job back due to an almost entirely unrelated bit of happenstance.
I took the "helmet" thing as the actors not wanting to run around in helmets all the time, sort of like how we see Tobey McGuire/Andrew Garfield's face waaaaay too much while in the Spider-Man costume.