I'm stuck on the boss demons gate in temple of the ancients but the strategy..

Use the item Phoneix Down on it. Since it revives your team it's a holy item, this mosters weakness is holy.It will kill it one hit but it rarely hits. So have everyone in your team use a Healing spell, or item.

Well if I were you I'd make your third party member Vincent and make sur ehe has his level 2 (Death Gigas) limit break. I would equip one of your characters with the summon Bahamut as it is very helpful. If Cloud has his Meteorain limit break you should have little trouble. Avoid usuing Fire, Earth and Pooison spells in this battle. Keep your characters healed and keep using both offensive and defencesive attacks. Barrier and MBarrier are also very helpful here.

Sorry! My first subbmission was wrong I thought you were talking about when you had to go through that cave with Red XIII's grand dad (don't remember name).

If you use Aeris, make sure her Healing Wind(I think that's the name) limit is equipped, and use it when needed. Aeris should mostly have magic to fight with(what I did). And having Vince is good insurance as well. What I did - didn't have Vince - was have Nanaki, Cloud, and Aeris as my party. I equipped Cloud with the least Magic Materia, had Nanaki have moderate, and Aeris had alot of magic. This worked for me.
Cloud's limits: Climhazzard, Blade Beam.
Nakaki's limit: Lunatic High
Aeris's Limit(sadly, only her first): Healing Wind.

Small miracle when I start to think about it. My characters survived not from strength, but from my strategy. Also, It would be good if you have a hearty stock of Items(restoritive).