THIS REVIEW IS MEANT TO BE READ AFTER YOU'VE SEEN THE EPISODE. I WON'T BE GIVING A PLOT SYNOPSIS FOR THE EPISODE AND I WILL BE REFERENCING SPECIFIC EVENTS, SO IF YOU HAVEN'T SEEN THE EPISODE THEN THIS WON'T MAKE MUCH SENSE.
Fight Fighters is simultaneously one of the simplest and most complex episodes of Gravity Falls. On the one hand its story is very simple, boiling down to Dipper stopping a monster who is basically Ryu from Street Fighter from killing Robbie. It doesn't sound that simple, but compared to the more mystery focused episodes of the show it really is. On the other hand though is the much more complex humor of the episode. It's not less weird or more sarcastic, but it is much more intricate. The simple plot mixed with the slightly different style of humor allows Fight Fighters jokes to excel, but like many other humor focused episodes it holds it back from being the show's very best.
Fight Fighters is much more reference based than any other episode of Gravity Falls, relying more on nostalgia and memories of the video games of old than the usual weirdness and clever dialogue of a normal episode. It still has that, but it definitely takes a back seat to the video game stuff. This is both a strength and a weakness, as the target base for the humor is much smaller than usual, especially among its large demographic of children. If you didn't grow up with the games of the 80s and 90s then this episode will still be funny, but not nearly as much as if you got all the jokes. I personally find this episode utterly hilarious because I did grow up with an understanding of old games, so I got all of these references (yes, even the "my car" one), but I can see how someone who didn't could find this episode's humor disappointing.
In a better episode these possible lost jokes would be balanced out by some good character moments or development, but Fight Fighters doesn't really have any. This is the episode that really starts to show the inherent weakness in Dipper's interest in Wendy as a dramatic plot, in that there aren't many ways for it to end. It's pretty much impossible for them to get together due to their age difference, so there isn't really any of the suspense that's usually present in a good "will they won't they" plot. That really only leaves Wendy letting Dipper down gently, as she's way too good of a person to kick him to the curb because of how he feels. Robbie only furthers this problem by being an uninteresting device to further the plot. He has literally no funny jokes in this entire episode, something that's painfully common whenever he's on screen in any episode of Gravity Falls, making his interactions with other characters very one sided, a bit like whenever Pacifica and Mabel spoke in Double Dipper. All these factors take basically all of the interest out of the main plot of Fight Fighters from a character standpoint, leaving it only with the jokes to hold it up. Those jokes are great, but without a good personal element behind them they feel unimportant. This is a problem that persists throughout the rest of season one whenever Dipper's pursuit of Wendy becomes the main dramatic focus, unfortunately making many episodes less interesting than they could be. Fight Fighters is really just the first episode to display this problem and it's probably the clearest example. Dipper and Robbie fight over Wendy behind her back, something supernatural happens, then by the end of the episode they just keep hating each other like nothing ever happened. The episode tries to make it look like something changed at the end because of their "cold war pact", but this is really just an extension of what they were already doing and it isn't ever mentioned in the show again.
Fight Fighters commits one more sin of Gravity Falls, and that's its criminal under use of Mabel and Stan. If they had an interesting and funny b-plot then that might make up for some of the narrative shortcomings of Dipper's main plot, but instead they get this out of nowhere thing about Stan's fear of heights. Their dialogue throughout it is funny and clever as usual, but there just isn't much for them to do. A good b-plot compliments the a-plot in some way, but it's basically by pure contrived coincidence that Stan and Mabel happen to be at the same place at the same time as Dipper and Robbie at the end of the episode. There's simply too much of a disconnect between Mabel's actions and Dipper's to make them seem like they belong in the same episode together and the episode suffers because of it. It's not utterly horrible due to the good jokes and funny moments, but it seems unfortunate that the show's two funniest characters have such little interaction with the monster of the week. Stan doesn't even see Rumble once and Mabel only gets one scene with him, which while hilarious, doesn't really seem like it's enough. It almost seems like Fight Fighters would have been better off foregoing a b-plot in favor of giving Mabel more involvement in Dipper's fight with Robbie. There are probably more possible jokes there and the entire thing would feel like less of a missed opportunity.
So it might sound like I don't like Fight Fighters, but that really isn't the case. I think it could be a lot better, but I still think it's good. As an episode to watch purely for its humor it's great, but only if you're a person who likes 80's games. I fit that target demographic, so I find it very funny, but if you don't hold any nostalgia for the days of Donkey Kong and Street Fighter than this is going to seem like a very disappointing episode of Gravity Falls.
-The pixel art in this episode is utterly fantastic and is easily one of the most visually interesting parts of the entire show. The way that the normal art style mixes with the new style is surprisingly seamless and it makes Rumble feel a lot more real than he would if he wasn't better implemented.