(I'm totally level 12/11 going into the Shinra Building, but I could certainly be lower. I would've earned Climhazzard by now, but... why would I do that onstream, right?)
I tried to defeat Ruby Weapon a month ago and I was destroyed so I'm curious about this superbosses and stats talk.
Well, for Ruby Weapon, I usually go in with 2 people KO'd so Ruby buries his arms right away (then cast Life2 on those people after he sticks his hands into the sand). You don't even need to be at a high level either, since you can probably beat it around Level 38 or so (iirc, Ruby's only at Lv 59).
There are several things you can do at this point. Never cast poison on the hands because that'll lead him to taking them out early and you don't want that to clean up.
Take Advantage of Paralyze
Ruby's weak vs Paralyze, lol.
Use Dazers. Use a lot of Dazers. Steal Dazers from the hedgehog enemy near the City of the Ancients/Battery Caps near Rocket Town, and clone them with W-Item or steal a whole lot of them.
Cast Slow on Ruby, too, so he won't be quick enough to get out of Paralysis status.
Cast Darkness/Blind on Ruby if you want to avoid his physical attack.
Cast Big Guard. Attack. Make sure he's paralyzed. It takes a while, but this is a pretty easy solution to the problem. He has 80000 HP, so have fun and put a podcast on in the background or something.
Magic Hammer
Go in with two people KO'd, have him bury his hands in the sand, revive with Life 2. Give everyone Ribbons.
Use Magic Hammer on Ruby. His MP isn't that high, so with 25 or so casts of Magic Hammer (3 casts per turn if everyone has E. Skill equipped), Ruby will be at a loss as to what to do.
Ruby Flame is fire-based, so it's best to keep Fire Materia + Lv. 3/Mastered Elemental Materia in your armour to absorb it.
After that, you'll just have the tentacles' HP drain/status effects to deal with, but that doesn't really matter. Ruby Ray can't be blocked, but having better armour around like the Ziedrich or Mystile equipped will probably stave it off. Cast Dragon Force for higher DEF. Attack with whatever you want. Knights of the Round, Quadra Magic, whatever.
Cheese it
Knights of the Round, Dazers, probably Mime. LOL.
See, if no one wanted to see FF7 in action, I would've chosen an FF8 Low-Level run instead since I'd equip Enc-None/Enc-Half just to keep things going in terms of narrative.