We've got an old school brawl going on in this round.
Superbosses Omega and Shinryuu (FFV): While there have been several optional super powerful enemies and bosses before FFV, Omega and Shinryuu are probably the first ones designed around playing smart as opposed to just beating them by the level race. Omega will test a player on how well they know their skill sets and what jobs the player has spent time in. Most players know about the Duel-Wield/Rapid Fire/Thundaga Sword combo; but how many of you know that the Bard class has the power to cast Stop on it? Shinryuu on the other hand tests how well you know how to beat a boss by just coming in with the proper gear. Granted Dragoons and some Time Magic is super useful, but not as much as Coral Rings, Ice Shields and the Dragon Lance. Omega especially is worth mentioning as being one of the first true optional bosses in the fact that it's easy to find, completely optional, and doesn't really net you anything of value outside of a silly bragging rights reward. In many ways, FFV introduced the more modern idea of what an optional superboss is.
VS.
Rydia's Summon Acquisition Bonanza: If you play FFIV normally, Rydia will acquire only six summons through her journey. Yet she actually has fourteen summons you can acquire over the course of the journey by exploring the worlds thoroughly and maybe getting lucky with an abysmal drop rate or four. Odin, Asura, Leviathan, and Bahamut are all completely optional and semi-story based summons you can challenge to win the honor of using them in battle, and most players know these four are a godsend. The last four are normal monster summons that drop from various palette swaps of the class, and while many of them seem pointless, all four are actually pretty useful if you know where to use them and somehow get them early enough,