Sorcerer in training
""The Secret Origin of Denzel Crocker" had Timmy and his fairies going back to 1972 and Timmy found out Cosmo and Wanda were Crocker's fairy godparents back then. It's unknown if past Cosmo and Wanda recognized their present selves but there were two Jorgens who even danced together."
I think Wanda recognized their past selves, but Cosmo... was Cosmo. Past Cosmo and Wanda don't remember because Jorgen pulled a Fairy Godparent Neuralizer on them. Present Timmy, Wanda, and Cosmo were also permanently banned from ever returning to that time period again.
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In the short story 'Forty, Counting Down' and its companion 'Twenty-One, Counting Up', Justin Kloster meeting his past self is the whole point. He wants to pull a set right what once went wrong. It doesn't work. But he does change his future, and his new future seems much brighter than the old. Summary here
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Wouldn't Mirai Nikki be a notable aversion to this trope? Just a heads up...this is a huge spoiler for anyone who hasn't seen the end of the series, so You Have Been Warned.
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To elaborate, in the Mirai Nikki canon, you can time travel, but doing so creates an Alternate Universe. Yuno is from a previous timeline/universe and came to "our" timeline and didn't just meet, but actually killed her 2nd-world self. Confusingly, characters in a given Alternate Universe are treated as the same person, except when they're not the same person. Very strange, and the most egregious instance of the Timey-Wimey (and Spacey-Wacey) Ball in action is in the epilogue after the Grande Finale, when Yuno-2 stabs herself, but Yuno-3 is given Yuno-2's memories to be co-god of the 3rd world with God!Yukiteru, and is apparently treated as the same person.
Edited by 69.172.221.4