I don't think it's very reasonable to make something like that with sprite tiles at all. The SNES has a hard limit of 256 sprite pixels per scanline, after that any further sprite pixels will simply not be rendered until the next scanline. The mecha koopa's lightning is 128 pixels wide, I think, and can already sometimes cause problems due to the sprite limit. There's a reason a beam like this (blizzard buffalo, mega man x3)
is just 1 color: it's made with windowing HDMA rather than sprite tiles (only the front and back of the beam are sprite tiles).
You can use sprite tiles to make this, but you're really fighting against the hardware. If you must, you should make the beam shorter to avoid sprite limit. Depending on how you make the beam, you might want it to be its own entity (like the mechakoopa does) or be completely controlled by the source entity (which i would guess blizzard buffalo's beam is). You *can* use cluster sprites but that seems like an awfully clunky solution. The beam is almost certainly just going to be a graphical effect with a single hitbox, which isn't really what cluster sprites are good at.
allow shy guy emojis in post footers you cowards!