Shiva (Final Fantasy V boss)

Shiva is an optional boss in Final Fantasy V. The party find her in Castle Walse's basement, where they challenge her. Upon her defeat, the party can summon her into battle.

Strategy
Challenging Shiva right away isn't a smart idea. For one thing, you won't have a Summoner yet, so even if you beat her, you still won't be able to summon her. Also, she is accompanied by three Ice Commanders who can easily kill an under prepared team.

If you do challenge her straight away, have Black Mages cast Fire while your Knights and Monks keep on attacking. Your first target should be the Ice Commanders. Once they're gone, you can fully concentrate on Shiva. However, she will be using spells like Blizzara, which will easily kill you if not prepared.

If you're willing to wait, come back after going to Karnak. You will now be able to use Fira and summon Ifrit to deal with her easily. You can also just break a Fire Rod to deal with her quickly.