If the player challenges Shiva before going to Karnak, the Ice Commanders might kill the team easily. To challenge Shiva as soon as possible, a Black Mage should cast Fire while the Knights and Monksattack. Ice Commanders can also be disabled with Sleep if the player can't kill them quick enough. Once they are gone, the party can concentrate on Shiva.
If the player has been to Karnak, Ice Commanders are easily killed with Fira and Ifrit.