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this is not really retconning. retconning is changing the past.
I GUESS technically it is taking place in the PAST but retconning is usually changing the way something happened, not adding something that hasn't shown up yet
so if you didn't believe energybending was a deus ex machina in the first place, what is something where they tried to retcon it later and it didn't work for you?
bioshock infinite, one character that used to be on your side (she's an extremist) threatens to kill some capitalist's kid because she believes that the movement has to be "pulled up by the roots". It's one of the stupidest moments in the entire game b/c your ally turns on your in 2 seconds. Then a year later the DLC revealed that actually somebody else was puppeting her and demanded that she do it. lol.