For some points on the plagiarism under the read more (what I collected/organized while building up an email to send):
1) TIMELINE
RGB was created long before, over a decade before Mr. Puzzles first debuted.
(*RGB's first appearance may have been 2011, was a little iffy on that)
2) UNDENIABLY UNCANNY RESEMBLANCE
The number of traits, some uniquely specific to and representative of RGB's design, that are copied in Mr. Puzzles design are too many to be chalked up to 'just a coincidence'
Especially when you look at the designs of all of the other TV head characters out there - I collected as many as I could find (though I'm sure there's more) and none of them come even close to sharing the number of similarities that these two do.
3) TV MODEL AND DESIGN CHOICES
While looking up references for older TVs, I found that for the exact TV they're based on (small retro box TV with knobs in the upper right of the TV and an antenna) most of the references didn't have a vent on the side of them like RGB and Mr. Puzzles do.
I looked up 4 different reference terms, and still had to scroll a while before I found one that matched exactly (above collection just a general sample/example of types of TVs I found). Unless my browsers are wigging out, either the pictures that would come up for these kinds of TVs were different in 2023, or this exact combination of features are just not very common for this style of TV. If that's the case, it may be a bit strange to design a character with those features together.
Here's where that distinction is important: Mr. Puzzles as a character doesn't have much of a reason to go with this design over other styles of similar TVs. But RGB does. The vents on the sides of RGB's head aren't just an aesthetic choice - they're included as a legitimately integral part of the story-line (Negative RGB). The same can be said for a number of other choices Modmad has made, down to individual items of clothing, that show just how much thought and intention and consideration went into every aspect of RGB's design.
Which makes it that much more frustrating to see him get plagiarized in such a careless manner by people who don't even seem to put much care into their own character (common criticism I've read that SMG4 fans have had about Mr. Puzzles and his 'arc').
4) OTHER PEOPLE, EVEN THOSE WHO HADN'T HEARD ABOUT THE SITUATION FROM MOD, NOTICED
This has been noted by fans of both series since Mr. Puzzles first came out.
Some people may have found more points than this, but these are what I stumbled upon. Hopefully helps bring a little more context to the situation.
gummygunk
izzy806
germansingergirl
vaporwave
amandla
ellievsbear
snowghoul
pixelskylines
andulkaphoto
yousharknotpass
blakekathryn
