Well, if anyone wants to implement these graphics:
the graphics (CHR) bank in an NES game is a 128x128 image that looks like this:
Every square there is a new 8x8 sprite.
Here's one of the sprite sheets from Karate Kid, followed by a background graphics sheet at bottom, which includes the title screen and the cheering crowd.https://imgur.com/a/5DHirs6
I pulled this using the Mesen emulator to look at the CHR banks in the PPU Viewer, modifying palettes to make it more visible.
So, to make your Cobra Kai graphics work in the actual game, you'd need to go through these 8x8 pixel tiles in Photoshop (maybe using the checkerboard image I posted as an overlay at low opacity), and compare them to a sprite sheet of the characters, and your modified version of that same artwork.
So for Elvira's Monster Party, I put together matching sprite sheets from the normal game and from your redesign. I then went through block by block, looked for each sprite block, found it, and pasted the modified sprite over it as a replacement layer.
This replaced art can then run in Mesen as an HDpack and can be pasted into the actual ROM using Tile Layer Pro or a similar program. (To do this I carefully change the color palette for the entire image to black, red, cyan, and white, invert it and save as 4-color BMP.)
To alter text in a game, I use the FCEUX emulator and open up the hex editor. I probably need to create a lookup table, or LUT. For Monster Party I used Oriton Table Creator. I looked at where the text font is stored in the CHR graphics, and noted the number of each sprite (using the PPU/CHR viewer in Mesen or FCEUX). So I create a lookup table which translates each letter in the font to the location of that letter in the graphics.
The number of tiles you use for your title screen should match those used for the original, since it will have to fit in the same space in the CHR bank. You may also have to duplicate the layout of the original, as its blank tiles may have to stay blank. Shiru's Screen Tool may come in handy, as may I-CHR.https://shiru.untergrund.net/software.shtml
Finally got the Monster Party title screen looking the way I wanted it to.
Boy, was THAT a lot of work.
NES Screen Tool was used.
Elvira's hair was blue in the design, but it's not possible to block that out within 16x16 NES restrictions.
I've released the Elvira hack and continued to tweak it.http://www.romhacking.net/hacks/5423/
(I have not updated the cutscene pointers, but did make some changes to boss text.)https://www.youtube.com/watch?v=WP_csuNh7u8
I've updated this hack to version 11. Due to crashes in the cave in Round 3, and in the boss rooms of Round 7, Mark and Birgon have been reinstated in these sections rather than Elvira. If I can figure out the exact sprite that's causing trouble I can reinstate Elvira. Cycling water palette lacks a dark color in Round 5.