There is a trick to tearing up emerald...

Get your chars HP to 7777

equip comet on one char and quadra magic linked

equip mime on other 2

Use lucky 7s to take a quarter of his hp then use comet with quadramagic and mime it and if hes not dead finish him with KOTR

ive never tried it but ive heard it works to be honest i havent played FF7 for a long time