Calciborite

@AndrewDavid That's pretty damn close to what I wanted. Now i just need to replicate that effect on the image I originally wanted to put it on, but since you've shown it's possible, it shouldn't be too hard. I hope. Tempting fate and all that. Thanks again.

@AndrewDavid Thank you. I think this might be what I need, though the automatic "warp to fit the selection" function is a bit of an issue; even with distortion set to zero there's some twisting going on if the image is larger than the selection area. Guess I'll have to fiddle a bit with the settings and see if I can reduce it further... Or just stop being a lazyass and start cropping, I guess? Heh. Anyway, thanks again for your help.

@Eli Thank you for the suggestion, but that solution sacrifices image quality and doesn't actually produce the visual result I'm looking for. I suppose chopping the effect image into chunks and basically using them like puzzle pieces might work, but while that would preserve image quality, it'd also complicate the process and I had hoped to avoid precisely that. I'd really just like it if the function simply pasted the image into the approximate center of the selection instead of doing so practically offscreen (why does it do that, anyway? I literally cannot see any reason why anyone would want that to happen, though I assume there must be one) or at least allowed the sliders to go further than -2 / 2. Guess we can't always get what we want. Still, I appreciate the advice.

@AndrewDavid Alrighty then. Please bear with me, as I am the noobiest of noobs with paint.net. The image is 1600 pixels wide and 235 high. Pardon the absolutely godawful pictures, they're something I threw up right quick as an example, nothing more. They match the general size and appearance of the actual image I worked on, though. First is the sword in its unaltered state. Second is the sword with the effect added to it via transparent layer. Third is a screenshot showing the effect + sword and the Fill From Clipboard slider. Fourth is the actual effect I used, some stock lightning effect I found somewhere a while ago (I had to re-save it as a crappy jpeg to not break the upload limit, sorry). The white center of the effect is what I'm trying to center onto the selection. Said selection is the blade of the sword only (on layer 2 with some transparency), selected with the magic wand tool. As I hope I've been able to show, you can see how the lightning effect refuses to be centered onto the selection and how you can only ever see the uppermost half/corner of it, since it pastes way out of focus for some reason my nooby self can't discern.

That's the problem. I can't position the effect. The sliders only go to -2 and 2, and that is just barely enough to partially move the image into the selection area, leaving most of it invisible.

Alright, after trying to use the Fill From Clipboard function, I've come to the conclusion that this plugin is either useless or I'm using it wrong. Since it's most likely the latter, could someone explain to me how you center the pasted image into the selection? I'm trying to use the Fill function to add an electrical effect onto another object and while I've got the selection, transparency, etc, down right, I just can't center the effect into the selection correctly. It pastes outside the selected area, so it's invisible until I use the slider to adjust it's position, but even using the slider, I just get a part of the image, usually the corner or upper half of it. The sliders stop at -2 or 2 and that's simply not enough. What exactly am I messing up here?