These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
"Funny Aneurysm" Moment: the revelation that Momo's father used to conduct experiments on chrysm ore in order to resurrect his dead wife; it makes the sight gag of finding his Porn Stash a little unsettling.
Game Breaker: The hybrid-Rei form is incredibly fast and has a guaranteed crit-strike ability. The Myrmidon is also ridiculously powerful, and both can be maintained longer than Kaiser. It also allows abuse of bonus EX turns with the Resist ability. Also, try this combination: Rei + Burglar Garb + Chain Formation.
Focus makes your next attack do 2x damage. If your next attack happens to be the same dragon form's Aura spell, you get another 2x damage multiplier on top of that. He ends up doing 2,500+ damage, where even Garr is hitting for puny 300-400s. He does all of this, in a humanoid form, by punching the enemy. No wonder that the power of the Brood is feared by Myria.
Although it's only of any use in a TAS, you can get up to 32 hits with Super Combo, which at that point out-damages everything else in the game by a large margin.
Rei's Weretiger ability normally makes him attack allies about every 1 out of 5 attacks, and he tends to do enough damage to kill them in a single hit unless they're particularly durable. Luckily, he's dumb enough to listen to the Influence skill, an otherwise useless ability you can use to sic weak enemies on each other, which ensures he will only attack a specified target as long as the target and the Influence-caster remain alive. While not the most powerful option for boss fights, it's certainly one of the easiest to set up and abuse.
Sidetracked by the Gold Saucer: Fishing, especially now that the game introduces Manillo merchants, who offer awesome rewards in exchange for fish that function as Disc One Nukes. note The first example being the merchant west of the Farm, who sells the Silver Knife, a weapon that will make the Bosses in the McNeil Manor complete jokes, in exchange for fish that can be found and caught with ease in the first two fishing spots.
Woolseyism: Some of the Dub Name Changes fall into this: the lumberjack Babadel was renamed like legendary lumberjack Paul Bunyan, the traitorous Zurusuru was renamed like the Norse Mythology's god Loki, the generic-named Great Wise Tree and Dragon God were given mythological upgrades into Yggdrasil and Ladon and the crystal/fossil pieces found around were switched from "Ghost" to "Chrysm".