Weight is 2.78g. There were experimental strikes at this weight (plastic patterns 42gr) It's not damaged or a rusted up one as I've seen in posts. I have several 1942 d pennies that all weigh correct 3.11 or within acceptable range Some of which are in way worse condition so I know it's not anything to do with that I do have several pictures and in a few of them I feel I see a pattern image in the coin itself I've been searching for answers for weeks to the point I made this account today lol so any help would appreciated I do not believe one of these have ever been discovered if it could be what I hope although I know there is probably a safe explanation to what I have I've only begun my life long love of coins a year ago so I'm still some what fresh.
The problem is the coin is copper and not plastic. Most of the plastic pieces were injection molded and wouldn't have survived being struck in a coining press. The reinforced resin "plastic" piece were struck but for the most part did not accept images well and would not have looked like a copper cent. I think you have a worn copper cent struck on a slightly rolled thin planchet and any "pattern" designs you are seeing are the result of numismatic Pareidolia.
I'm not sure what you mean by "struck over 1942 canceled plastic pattern". Your coin is only about 11% light so that's not definitive evidence of some other composition. None of the 1942 experimental cents have mint marks or were struck in Denver so that makes this coin highly unlikely to be anything other than a lighter than normal regular cent. You could have somebody do an XRF on it to determine composition if you wanted to I guess.
Buy a copy of Roger Burdette's book "Patterns & Experimental Pieces of WWII" to further your interest/knowledge.
It may not be plastic that's just the only weight I could find that matched. so definitely could be something else. it's not a thin penny it's all I'll post a pic of another 1942 d that has more wear on it then this yet is still above 3.05g . Have y'all heard of any thin rolled coins that weigh this low ? I'm .2 under the low tolerance of 2.98 for