Ruby and Emerald are amongst the easiest superbosses in any FF.

Ruby is weak to Paralyze, and when I say weak, I mean stupidly, pathetically weak. Just 20 Dazers are enough to get you through the battle without him even attacking you. Alternatively, you could use Hades summon to put other plethora of status effects on him as well. I've seen him getting confused, poisoned, sleeped and Paralyzed. That's pathetic for a superboss.

Emerald is weak to Gravity, so you can just use W-Magic + Quadra Magic - Demi3 + Mime, so that everyone does 8 x 9999 hits per turn, which is a lot faster than to cast KOTR over and over again. Equipping Final Summon - Mastered Phoenix guaranteed you an auto ressurection should things go awry, which rarely did, since his only strong attack Aire Tam Storm does 1111*nº materia equipped and since at most you'll have 4 materia equipped, 4444 damage is pretty manageable.

All I'm saying is that by abusing Zell's Limit Break I killed Omega Weapon in three turns, though there was also a Lionheart thrown in there.

I never bothered leveling my Materia enough to make killing Emerald or Ruby viable.

I hear you on Omega Weapon, that one was also pretty easy as well. Almost all FF superbosses have some cheap way to defeat them easily, the only exceptions I can think of are Omega, Shinryu from FFV and Zodiark from FFXII.

There's an "easy" way to beat Yiazmat?

I've heard of an easy way to kill Zodiark, though it requires a bit of luck and good timing for before he puts up the Paling....

Yiazmat isn't even hard, the battle against him is just a long wind up grind that requires patience. There's no "easy" way to do it, but you can streamline the battle to do it in less than 3 hours with the Darkblades and Haste.

That easy way to kill Zodiark just involves getting up a Quickening combo up to 12 hits and getting anything above Ark Blast, in order to kill him before he uses paling. You'll still have to bear 200K of his HP in order to get there, and with his constant spamming of 50% OHKO party Darkja (25% using Demon Shields or Shell) and spamming of Scathe and Scourge, the battle can end pretty quickly even before you get to his half health.

Plus, if you die, you'd have to start all over from the latest Save Point in the Henne Mines and the one closest to Zodiark still takes you at least 30 minutes to get to him once again.

You.... you are very familiar with this stuff!

My wife is the one who killed all the optional bosses.

I never killed anything bigger than Fafnir.

*sob sob sob sob sob*

I've replayed FFXII three times now, I'm pretty familiar with almost everything the game throws at you xD 

I even had a farming craze on my third playthrough in order to get three copies of each of the "Ultimate" weapons for each category (except Zodiark Spear. I ain't touching that frigging 0,1% probability chest in my life >_>).

Next playthrough i'm going to make it Bow/Gun exclusive. Fomalhauts when used properly are pretty much the most devastating overall weapons in the game.