Just managed to beat emerald weapon without spamming W-Summon KOTR and Mime, using emerald own weaknesses against him. Quadra-Magic - Demi3, will give you 4 attacks of 9999 almost during all stages of the battle, even if he halves Gravity magic, due to his high HP.
Also using 4x Cut as primordial physical attack, backed up with Big Guard and White Wind, and you can slow and darkness him as well (use the item Ink, it's almost 100% effective).
I didn't use any of the ultimate weapons on my team (Cloud, Barret and Yuffie) because those 50k AP he gives are a huge boost to your materia.
Ruby comes next, going to try utilizing the Paralyze (Dazers) - 4x Cut combo on him.
Current PC Build
CPU - i7 8700K 3.7 GHz (4.7 GHz turbo) 6 cores OC'd to 5.2 GHz with Watercooling (Hydro Series H110i) | MB - Gigabyte Z370 HD3P ATX | Gigabyte GTX 1080ti Gaming OC BLACK 11G (1657 MHz Boost Core / 11010 MHz Memory) | RAM - Corsair DIMM 32GB DDR4, 2400 MHz | PSU - Corsair CX650M (80+ Bronze) 650W | Audio - Asus Essence STX II 7.1 | Monitor - Samsung U28E590D 4K UHD, Freesync, 1 ms, 60 Hz, 28"
